HKMetS BULLETIN, Volume 1, Number " 1991

HONG KONG METEOROLOGICAL SOCIETY About the cover

The cover picture shows a G.M.S. colour enhanced picture of Typhoon Yancy around noon on 18th August, 1990, the hottest day ever recorded in Hong Kong

The Hong Kong Meteorological Society EDITOR-in-CHIEP Bulletin is the official organ of the Society. devoted to editorials, news, Bill Kyle articles, activities and announce­ ments of the Society. EDITORIAL BOARD Members are encouraged to send art­ cles, media items or information for Johnny C.L. Chan publication in the Bulletin. For guid­ Edwin S.T. Lai ance please see "INFORMATION Andrew Lockert FOR CONTRIBUTORS" in the inside Glenn McGregor back cover.

The Bulletin is copyright. Penniss­ Views expressed in articles or ion to use figures, tables, and brief correspondence are those of extracts from this publication in of the writers and do not necess­ scientific and educational work is represent those of the Society. hereby granted provided that the The mention of specific products source is properly acknowledged. or companies does not imply Any other use of material requires endorsement by the Hong Kong the written permission of the Hong Meteorological Society in pref­ Kong Meteorological Society. erence to others which are not mentioned.

Published by ~ The Hong Kong Meteorological Society

c/o Royal Observatory, 134A Nathan Road, Kowloon, Hong Kong. HKMetS BULLETIN, Vol. 7, Number 7, 7997

HONG KONG METEOROLOGICAL SOCIETY BULLETIN

CONTENTS

Editorial 2

Research in the atmospheric sciences in Hong Kong - a proposed agenda 3 Johnny c.L. Chan

"SPECTRUM" : typhoons under critical examination 7 c.Y. Lam

Storm period variation of rainfall pH: the example of Typhoon Brenda, May 1989 10 Mervyn R. Peart

An analysis of tide gauge and storm surge data in Hong Kong 16 Wyss W.S. Yim

News and Announcements 24

Correspondence 26

Hong Kong Weather Reviews 27

Meeting Reviews 36

Calendar of Coming Events 41 Editorial

On the special occasion of the inaugural issue 4 Society. With this in mind an Editorial Board the Hong Kong Meteorological Society Bulletin the Editori­ was formed and after a considerable gestation al Board has invited Mr. P. Sham, foun ding Chairman of period produced the "new baby" which you are the Hong Kong Meteorological Society, to write this first now holding. Editorial. As founding Chairman of the Society it gives me great pleasure to write this inaugural Editorial. A glance at the contents page of this first issue will provide you with a good idea of the range of material which the Editorial Any new venture, whether it be a new Board hopes to include in forthcoming issues of job, a move to a new home, or even a new the Bulletin. The publication of articles which hobby presents opportunities as well as risks. serve to inform members of progress being The satisfaction which one derives from suc­ made in the profession is clearly of great cessful p art ic ip at ion in such ventures often importance but the capability to act as a forum stems from the way in which we handle these for members views and as a vehicle for news two complementary attributes. You are now and reviews of Society activities is also seen to reading the first issue of the latest venture by be of considerable value. the Hong Kong Meteorological Society. The level of satisfaction which you express with the The Editorial Board recognizes, finished product will be a measure of how however. that not all our members are profes­ successfully the Editorial Board has balanced sional meteorologists and so they need to ascer­ the opportunities and risks associated with its tain what your interests and needs are. They production. are aware that a reader's trust and respect must be earned and fully intend to do their The Society itself is a new venture. part. You can help them by turning the rela­ being registered in accordance with the provi­ tionship into a dialogue. Let them know what sions of Section 5 of the Societies Ordinance you think of the Bulletin, what you want most just over two years ago, and holding its inau­ to see on our pages. Like you, they are eager gural meeting in March 1989. It has had to listen and learn, to make each issue better moderate success in its first two years of exist­ and more responsive to the needs and aspira­ ence with the growth in membership being tions of members than the previous one. better than expected. The Executive Commit­ tee feels that this has been achieved by sustain­ I hope that you find this first issue of ing the interests of members by the variety of the Bulletin interesting and informative and, activities organized throughout the year. through your continued support. the harbinger These have included a Special Topics Lecture of many successful issues to come. Series, three Research Forums , and a Puhl ic Lecture Series. However, it has been felt for some time that it was essential for the Society • to publish a regular magazine devoted to news. - articles, activities and announcements of the Mr. P. Sham. Chairman

2 flKMeJS BULLETIN Vol. I, No. I, 1991 Johnny C.L. Chan Department ofApplied Science

City Polytechnic ofHong Kong

Research in the atmospheric sciences in Hong Kong - a proposed agenda

ing on research problems related to atmospheric science. Introduction This paper discusses a number of impor­ tant topics in atmospheric science wh ich are Research in the atmospheric sciences in Hong likely to be of interest to local scientists and Kong probably started towards the end of the last proposes the type of research that could be car­ century after the Royal Observatory (RO) was ried out. It is hoped that such discussion can established (Royal Observatory, 1989). Although generate more ideas so that research in the some occasional collaboration does take place atmospheric sciences in Hong Kong can continue between the RO and local or overseas institutes, to grow and eventually become respectable in the most of the research has been performed at the international community. RO. This situation has arisen because local ter­ tiary institutes do not have departments special iz­ Hong Kong, situated near the Tropic of ing in atmospheric science. This is a conse­ Cancer, is intluenced by weather both from the quence of the fact that the RO has been the only tropics and the mid-latitudes. Research in place where such graduates could go but its weather phenomena affecting Hong Kong yearly intake of these graduates was too small should therefore he divided into these two to justify setting up departments with this categories. However, such a division is not so special ity. clear-cut at times. For example, the severity of a cold surge can be influenced by the approach of a However, the situation has heen slowly typhoon te.g.. Chan. 1988a) while the track of a changing during the last few years. Concerns typhoon can also he modified by a cold surge over the environment and cl imatic change have (e.g., Chan, 1988h). Therefore, in the following led to increased research in these areas in the sections, the issues are grouped according to the tertiary institutes by scientists of related disci­ time scales of the weather phenomena. The first plines. Consultant companies dealing with envi­ section discusses the problem of nowcasting. The ronmental problems have also mushroomed. applicability of current numerical-weather-predic­ Graduates with knowledge in atmospheric or tion (NWP) models to medium-range forecasting environmental sciences can find employment in is then addressed. Because of their overwhelm­ these companies or even form their own! ing importance to Hong Kong, tropical cyclones Academic departments which provide training in are separately discussed in the section after that. these areas are also being set up in some local The hot topic of long-range weather forecasting tertiary institutes. At the same time, conservative and climatic change is discussed next and finally, budgeting by the government has limited the a summary is presented. amount of resources available for its departments to carry out research and development work. Thus, research in the atmospheric sciences in Nowcasting Hong Kong appears to be taking on a new dimen­ sion. Cooperative research projects hetween the RO (and possibly other government departments) Nowcasting (or sometimes referred to as very­ and local tertiary institutes are on the increase. short-range forecasting) is usually defined as More scientists in these institutes are also work- forecasting of weather with a time-scale of 0 to 6

JJKMelS BULLETIN, Vol. 1, No.1, 1991 3 hours. Tropical convective systems can be con­ (Chan, 1989) or global numerical models (Chan, sidered as the most important phenomenon in this 1988a). While improvements on the regional category as far as Hong Kong is concerned. model of the RO continue to be made (Chan, These systems, which have spatial scales of 20 to 1989), the performance of these regional and 200 km (the meso-beta scale as defined by Orlan­ global models under different situations should be ski, 1975), can develop within a couple of hours analyzed. That is, questions such as "when and produce copious amounts of rain due to the should I believe the predictions from this model" high mixing ratio of the tropical atmosphere. need to be answered. Methods to predict the Mesoscale convective elements developed within forecasting skill of numerical models have been rainbands of tropical cyclones also fall in this developed (e.g., Leslie and Holland, 1990) and category. could be appl ied , This type of research is not necessarily of a purely operational nature. To be able to predict the development Analyses of the model performance can provide of these meso-beta convective systems, one clues as to how a model can be improved. The must first understand the physical processes model-generated data (both anal yses and prog­ responsible for such developments. While the noses) can be considered to be extra information tropical atmosphere is conditionally unstable for the understanding of the physical processes of (e.g. Riehl, 1979), a triggering mechanism is these medium-range weather phenomena. often necessary for the initiation of convection. Possible mechanisms include (a) the destahil i­ To the more theoretically-minded scien­ zation of the boundary layer due to daytime tists, the dynamics of some of these weather heating over land leading to convective over­ systems may also be of some interest. For turn ing, (b) low -I eveI d Ynami caI up lifting example, during a surge of the northeast monsoon either from convergence associated with the in the wintertime, the cold air moves along the synoptic-scale flow or due to land/sea breeze eastern coast of China at a speed far exceeding convergence, (c) upper-level divergence caused that explained by normal advection. Gravity­ by transients on a synoptic scale, or (d) a wave propagation has been proposed as a possible combination of some or all of these mecha­ mechanism. Coastal Kelvin waves could also be nisms. involved. Research on these types of problems could eventually lead to an improvement in fore­ If the mechanisms responsible for the casting the arrival of such surges. different types of convective systems can be identified, it might be possible to predict the occurrence and development of these systems. Tropical cyclones Identification of such mechanisms will also provide a better understanding of the physical processes involved. This can perhaps help in Every year, about six tropical cyclones threaten improving the performance of me so scal e Hong Kong (Royal Observatory, 1988). An models by incorporating such processes into accurate forecast can lead to tremendous savings the models. Research in this area will involve in life and property. Unfortunately, our under­ the study of a large number of previous cases standing of the physical processes of tropical to identify the triggering mechanisms. The cyclone (TC) motion and intensity change is far recent study by Shun (1989) is a good start. from complete. As a result, improvements in the Applying a mesoscale model such as that used prediction skill have been slow although recent at the RO (Yeung et al., 1989) to test hypothe­ studies indicate that global NWP models have ses related to the different triggering mecha­ some skill in TC forecasting (Reed et al.,1988; nisms is also important in the understanding of Morris and Hall. 1988: Chan and Lam, 1989). the underlying physical processes. The same question posed in the last sec­ tion on the performance of NWP models can also Medium-range forecasting be raised in this connection. In this case, analy­ ses of model performance in pred i ct ing TC motion and intensity change can he made. Re­ This may be defined as forecasts in the range of sults of such a study are not limited to helping the one to five days. Weather systems in this catego­ forecaster to decide when to use the predictions. ry which affect Hong Kong include tropical cy­ they can also po i nt to the weaknesses of the clones, easterly waves and equatorward exten­ model so that improvements can be made (e.g., sions of mid-latitude frontal systems. Predictions Chan et 01., 1987). Because TCs occur over the of the behaviour of these systems have had Iimit­ ocean where data are scarce, model analyses and ed success with the introduction of the regional prognoses can he considered to he extra data

4 IIKMelS IIULLRTIN Vol. I, No. I, 1991 sources in diagnosing the physical processes has been done locally in this respect until the last leading to the development/decay ami movement few years. Research on the variability of temper­ of the model vortex. ature. rainfall or tropical cyclone tracks may lead to the development of seasonal forecast tech­ On the more theoretical aspects, the niques. It will also improve our knowledge of the dynamics of tropical cyclone movement needs to climatic variations in this part of the world so that be studied much more. While studies using any issue on climatic change (such as the recent simple barotropic or barocl inic models are obvi­ discussions on the greenhouse effect and sea-level ously necessary, analyses of observations could rise) can be addressed with greater confidence. also lead to new understandings. During the summer of 1990, four different experiments were carried out in the western North Pacific to study Summary tropical cyclones (Elsberry, 1989). These will provide the best data set ever for this region and will be available during 1991 for interested scien­ Research in the atmospheric sciences in Hong tists. They should therefore provide many oppor­ Kong has always been handicapped by the lack of tunities for tropical cyclone research in this area. enough academicians in the field. However, the growing concern over the environment and cli­ matic change has led to an increase in the number Long-range forecasting of cooperative projects between the RO and scien­ tist in local tertiary institutes. This paper has and climatic change proposed a number of topics which the author believes should be addressed. The topics are not meant to he exhaustive. In fact, topics which are Over the last decade, much attention has heen primarily of operational interest have been left focussed on the seasonal or interannual variability out because meteorologists at the RO should be of the tropical atmosphere. In particular, the the people most suited to perform research in amount of international research on the El these problems. In any case, it is hoped that the Nino/Southern Oscillation and the 40-50 day (or proposals presented here will bring about further 30-60 day) oscillation has grown tremendously, cooperation among the various organizations with and this has progressively improved our under­ an interest in atmospheric science in Hong Kong. standing of these phenomena. However. not much

HKMelS BULLETIN Vol. I, No.1, 1991 5 References

CHAN, J.C.L., 1988a: The intense ELSBERRY, R.L., 1989: ONR RIEHL. H .. 1979: Climate and cold surge of November 1987 affect­ Tropical Cyclone Motion Research Weather in the Tropics. Academic ing the south China coast. Paper Initiative: update on lield experiment Press, 611 pp. presented at the Guangdong-Hong planning. Interim Report. Naval Kong Seminar on Hazardous Post g rad s.«. NPS-63-90-002, ROYAL OBSERVATORY, 1988: Weather, April 10-13, Guangzhou, Monterey, CA 93943, 63 pp. Tr op ic al cyclones in 1988. Royal China. (in Chinese) Observatory, Hong Kong, 89 pp. LESLIE, L.M. and G. HOLLAND, CHAN, J.C.L., 1988b: Forecasting 1990: Predicting regional forecast ROYAL OBSERVATORY, 1989: the track of Typhoon Nina (8722) skill using single and ensemble Cat alog u e uf Publications. Royal Paper presented at the Guangdong­ forecast techniques. Submitted to Observatory. Hong Kong, 76 pp. Hong Kong Seminar on Hazardous Mon. Wea. s.« Weather, April 10-13, Guangzhou, SHUN, C.M., 1989: Meteorological China. (in Chinese) MORRIS. R.M. and C.D HALL, conditions associated with the occur­ 1988: Forecasting the tracks of rence of a waterspout in Hong Kong CHAN, J.C.L. and H LAM, 1989: tropical cyclones with the UK opera­ in August, 1988. Paper presented at Performance of the ECMWF model tional glubal mod c l. ESCAP/WMO t h e Gu a ngd o ng-Hong Kong Joint in predicting the movement of Typhoun Comm. Ann. Rev., Typhuol1 Seminar o n Hazardous Weather, Typhoon Wayne (1986). Wea. Cornrn. Secretariat. UNDP, Manila. October 20-21, Hong Kong. Forecasting, 4, 234-245. Phillipines, 102-105. YEUNG, K.K .. WL. CHANG & B. CHAN, J.C.L., B.J. WILLIAMS ORLANSKI. I, 1975' A rational WAN, 1989: Numerical simulation and R. L. ELSBERRY, 1987: Per­ subdivision or scales Ior atmospheric o I' mesoscale meteorological phenome­ formance of the Nested Tropical process. Bull. AmI:'/'. Meteor Soc.. na in Hong Kong. lnt. Co nf. on E. Cyclone Mod e l as a function of 56, 527-530. ASIlJ & W Pacific Meteor. and Clim .. storm-related parameters. Mon. P Sham and C.P. Chang (Eds.), W!a. Rev., 115, 1238-1252. REED, R.J., ACK. HOLLINGS­ World Scientific, Singapore. 451-460. WORTH. WA. HEDLEY and F. CHAN, Y.K., 1989: The operational DELSOL.1988 An evaluation of the analysis scheme and limited area performance of the ECMWF opera­ model in Hong Kong. Int. Conf. on tional system in analyzing and fore­ E. Asia & W Pacific Meteor. & casting tropical easterly wave disturb­ Clim., P. Sham and C. P. Chang ances over Africa and the Tropical (Eds.), World Scientific, Singapore, Atlantic. Mon. Wea. s-v. 116, 824­ 429-438. 865.

6 IIKMctS IIUILHTlN VIII. I, Nil. I, 1991 c.l: Lam Royal Observatory

Hong Kong

"SPECTRUM" - Typhoons under critical examination

This paper describes the background to SPECTRUM and some of the details of the data acquisition programme. It then outlines what is hoped for in terms of analysis of the data and Introduction issues an invitation to local scientists to apply the data to their ongoing or future research so that the opportunity to use such valuable data is not to be missed.

To mark the commencement of the International Decade for Natural Disaster Reduction. the most The need to observe typhoons comprehensive observation programme ever mounted by the meteorological community to study typhoons took place in the western North Typhoons annually bring a lot of damage to the Pacific in August and September of 1990. Under members of the Typhoon Committee, either the auspices of the ESCAP/W MO Typhoon through direct hits or through indirect effects Committee", seven members, viz. China, Hong such as heavy rain brought about by the modifica­ Kong, Japan, Malaysia, Philippines, Korea and tion of synoptic patterns by the presence of a Thailand, jointly conducted a SPecial Experiment typhoon. Accurately predicting the tracks of Concerning Typhoon Recurvature and Unusual typhoons is a key element in the warning opera­ Movement (acronym: SPECTRUM). During the tion to reduce the extent of damage. Global same observation period the United States and the numerical weather prediction (NWP) models are USSR carried out separate, but complementary, increasingly capable of representing and forecast­ observation programmes in the same geographical ing typhoons realistically and usefully. However, area. Taken together, these programmes pro­ front-line forecasters are all too aware of occa­ duced an assembly of data of unprecedented sions when typhoons move in directions markedly resolution and areal coverage, describing both the different from those indicated by NWP models, large-scale environment surrounding typhoons as especially in recurvature situations or when the well as their individual circulation characteristics. environmental steering is weak. While inade­ Exciting possibilities lie ahead for meteorologists quate data over the ocean might be partially to delve into the data and to find out what con­ responsible for some of the "wrong" predictions, trols the movement of typhoons. it is also apparent that there are gaps in our understand ing of the mechanism of typhoon movement. To address this problem, it is neces­ sary to generate a comprehensive observational data set covering several typhoons which are * ESCAP/WMO Typhoon Committee is a difficult to forecast operationally. Subsequently, committee jointly sponsored by the Economic and analysis can be carried out to evaluate the impact Social Council for Asia and the Pacific (ESCAP). of data on forecasting accuracy as well as to a United Nations body, and the World Meteoro­ elucidate the details of the physical mechanism of logical Organization (WMO). typhoon movement. This is the primary motiva­ tion behind SPECTRUM.

IlKMetS HULLETlN, Vol. I, No. I, 1991 7 0E IOOOE 1100E IJO"E I£OOE 150 £ooN • I • • • I • • • • • :t • I • 0 I • • I • • I • • I I • • • 0 • lOON • , • ,, • • Ii) , • , • 0 • , • • • ., I US, 11 • , • • , Ii\1 , :! :1 , 200N It , us 0 -1­ -- - -.__• , us ,, .ft ,, us us• ,, , .us• '. ,/US /~ / SrECTRUM AREA , OF INTF.RfST 00 L.-_--"'..L----'=-__---'L..L.. ...L..---"':....::....;:.....:.=.._--IL..:.-..L.L... -'- --'

Figure 1 SPECTRUM observations: upper air soul/ding station (circled dot - 6-ho/lrly, dot- l2-hourly); weather ship (solM triangle); buoy (flagged); wind profller (solid arrow). Also shown are US and USSR weather ships (open triangle); US upper-air sounding stations and wind profilers (open arrow). The track of Typhoon Yancy (9012) is also shown. That part ofthe track covered by SPECTRUM and Chinese lOPs is shown as a continuous til/e.

subtropical ridge or movement in weak environ­ The experiment mental flow, Throughout the SPECTRUM peri­ od, the experiment centre maintained operational contact with Members' operational centres which The overall objective of SPECTRUM is "to oversaw SPECTRUM activities within each obtain enhanced meteorological observational Member's territory. While the experiment centre data required for studies by Typhoon Committee kept the Members informed about its intentions Members on the movement of tropical cyclones regarding lOPs, Members were also given the in the western North Pacific with a view to opportunity of letting it know their individual improving operational tropical cyclone forecast­ assessments of the synoptic situation. ing" . The key component of the enhanced The Typhoon Centre operated by the observation programme during the rops was 6­ Japan Meteorological Agency played the role of hourly upper-air observations made at more than the SPECTRUM experiment centre. It was forty stations on land and on board two weather responsible for identifying target tropical cyclones ships (Figure 1). The spatial distribution of these and activating intensive observation periods observations was planned in such a way that (lOPs), following guidelines establ ished by an would maximize their usefulness in future re­ international SPECTRUM Steering Group. A search work. Hourly surface observations were tropical cyclone would be selected onl y if it also made by some 230 synoptic stations during would persist for 2 - 3 days at least as a severe rops subject to certain additional criteria. tropical storm, would cross a pre-specified target area, and would serve as an example of recurva­ Over the sea, voluntary weather observ­ ture or movement close to a weakness in the ing ships were requested to make 3-hourly obser-

8 JlKMelS IIUU.ETlN Vol. I. No. I, 1991 vations during lOPs. Weather buoys and off­ data set is being assembled by RSMC Tokyo shore platforms also contributed to this data Typhoon Centre based on GTS messages and gathering effort. add it io nal data on tapes sent by participating Members. A data catalogue is also to be pro­ Apart from conventional observations, duced to help interested researchers locate various modern technology was also brought to bear on data sets of a more specialized nature which are SPECTRUM. The Geostationary Meteorological held by individual Members. A comprehensive Satellite (GMS) was operated to yield more cloud data set embracing the results of SPECTRUM and wind vectors at both high and low levels. Further the other experiments will be generated by the US to the enhancement of conventional radar obser­ experiment group and will be made available to vations, a doppler radar was operated at Miyake­ the SPECTRUM research community by late jima. A wind profiler which gave vertical pro­ 1991. files of upper air winds with high temporal reso­ lution was operated at the Meteorological Re­ With inputs from operational forecasters, search Institute at Tsukuba, Japan, during lOPs. the SPECTRUM Steering Group met in December 1990 to review the forecasting problems encoun­ Most of the enhanced observations were tered during the lOPs and to identify the associat­ transmitted to Tokyo immediately via the ed scientific issues. It is intended that the results international meteorological telecommunication of that review will be brought to the attention of network called GTS. Special real-time monitor­ researchers in the region. The hope is that re­ ing procedures were implemented to ensure that searchers from institutions of higher learning will all relevant bulletins would arrive in Tokyo on be actively involved. to supplement the contribu­ time. tions from the meteorological services.

During SPECTRUM, a total of seven As a modest form of motivation, ar­ typhoons were intensely observed. They were: rangements will be made for the results of their Winona (901l), Yancy (9012), Abe (9015), Dot work to be reported in the Typhoon Committee (9017), Ed (9018), Flo (9019) and Gene (9020). annual reviews and to he presented in a technical Among them, Yancy will be long remembered hy conference to be held in China in late 1991. weather forecasters for its erratic track. especialIy Further opportunities also exist. including the the rare, if not unprecedented, feat of landing in third WMO International Workshop on Tropical China's Fujian province three times in three days Cyclones tentatively scheduled for late 1993. To before finally dissipating inland. Yancy's beha­ the extent possible, exchange visits of researchers viour after making landfall fully vindicated the and attachment of scientists from Typhoon Chinese programme of extended lOP's. For committee Members to advanced centres will also many years to come Yancy will be the perfect be supported. Th is is to facil itate the develop­ typhoon for meteorologists to study. In th is ment of scientific ideas and the effective execu­ respect, SPECTRUM was extremely fortunate in tion of research projects. being able to acquire so much data on a most unusual typhoon. Al I interested parties who see some possibility of applying the data generated by SPECTRUM to their ongoing or future research Looking forward are invited to contact C. Y. Lam at the Royal Observatory with an expression of interest to­ gether with an indication of the broad subject area While the more visible data collection phase of of your intended use of the data. Detailed ar­ SPECTRUM is now completed, the subtle process rangements can then be made to plan future of transforming the data into applicable knowl­ research. edge has just begun. As a first step, a quick-look

9 HKMe/S llULLEHN Vol. I, No. I, 1991 Mervyn R. Peart

Department of Geography & Geology

University ofHong Kong Storm period variation of rainfall pH: the example of Typhoon Brenda, May, 1989

May, 1989 provided an ideal opportunity to study ABSTRACT storm period variation in rainfall pH. The results are presented below.

Within storm variation of rainwater pH has been described for Typhoon Brenda which affected Typhoon Brenda Hong Kong in May 1989. Some suggestions have been offered to account for the results. A limited comparison with other" extreme" events Typhoon Brenda began as a tropical depression is also made. on May 16th, 1989, over 1000 km east-southeast of Manila in the Pacific Ocean. Landfall was made by Brenda in the Philippines early on May 17th and that evening it entered the South China Sea. Typhoon Brenda affected the South China Introduction coastal areas from May 19th to 21st. The ty­ phoon made landfall on the coast of Guangdong some 130 km southwest of Hong Kong. The Precipitation which has a pH of less than 5.6 is Royal Observatory (1989) reports that Brenda often referred to as acid rain. There is consider­ deposited 322.8 mm on May 20th at the Observa­ able evidence that much of the rainfall occurring tory and that this is the second highest daily in Hong Kong is acid rain (e. g. Tang, 1981; rainfall total ever recorded for May. It is also the E.P.D., 1986, 1989). The deleterious effects of eighth highest daily total for all months. Other this upon the environment are reviewed by, for areas of Hong Kong received even more rainfall. example, Gorham (1976) and Babich (1980). For example, 382.5 mm were recorded on May 20th at Sek Kong. Investigations into acid rain have, in general, reported values based upon a storm by storm, daily, weekly or longer, sample collection Data Collection periods (e.g. Skartveit, 1981; E.P.A. 1985, McColl et al . 1982; Tang et at. 1987). In comparison there have been few investigations The investigation was based at the Kadoorie into within storm variations in precipitation pH. Agricultural Research Centre, University of Hong Studies such as Pellet et at. (1981) illustrate how Kong which is located near Sek Kong in the New useful storm period pH data may be to investiga­ Territories. The location of Kadoorie is shown in tions into acid rain. Storm period sampling may Figure 1. be of considerable value in elucidating the con­ trols upon the pH of precipitation and in the Rainfall samples were collected at hourly interpretation of stream or river water pH values, intervals from 0800 hours on May 20th to 0900 especially those obtained during storm hydro­ hours on May 21st. The samples were collected graphs. in a polyethylene container. This simple, open collector, had a diameter of 19 ern and the lip The occurrence of Typhoon Brenda in was approximately 25 cm above the ground.

10 I1KMelS IWU-BTIN Vol. 1, No.1, 1991 N I I. t i

II )1 ,. " , 1 a j o i I I _ Major built-up area l

(:;:;:;::1 Area over 100 metres o d o 2 4 6 8 10 km ~ I I I I

Figure 1 Location of the Kadoorie Agricultural Research Centre in llong Kong, the data collection site,

A Casella tilting siphon rain gauge fitted with a from 5.0 to 5.6. However, from 0200 hours on 24 hour chart was used to record rainfall at May 21 st rainfall pH becomes more acid with Kadoorie. Hourly values of rainfall were ab­ values generally being below pH 5.0. The lowest stracted from the chart for May 20th and 21st. recorded pH value was 4.71 for the rainfall which No data on wind speed or direction is available at occurred between 0500 and 0700 hours on May Kadoorie. Therefore, data on wind direction 21st. were obtained from the Royal Observatory.

After collection the rainfall samples were Discussion taken to the laboratory where pH was determined as soon as possible. The sample pH was deter­ Some researchers have found that within a storm mined on the unfiltered sample using a Radiome­ event rainfall pH may increase with rainfall ter meter with a glass electrode. The meter was amount (e.g. Pellet et at. 1981). These authors calibrated using standard buffers of pH 4 and 7. also report that for event based sampling, rain­ water pH exhibits a significant positive associa­ tion with volume of precipitation. Furthermore, Results the E.P.A. (1985), on the basis of weekly sam­ pling, also report that acidity relates to rainfall amount. They suggest that this may be explained Figure 2 depicts storm period variation in rainfall by larger quantities of rainfall washing out more pH during typhoon Brenda. For much of the atmospheric acid ity. Rainfall amount may, there­ period from 0800 hours on May 20th to 0100 fore, exert an influence over acidity and pH. hours on May 21st the pH values are in the range However, the E.P.A. (1985) found a poor corre­

/lKMetS BULLETiN Vol. I, No. I, 1991 11 150 -

Q) Q) -~

Q) Q) - 8-100 - c: - u0 Q) ~ Cl '0 - c: 50 ~

0

6

~ Q) 1ti ~ c: 5.5 "(ij a: -0 J: 0. 5

4.5

70

60 -E 50 E - 40 ctS c: 30 -"(ij a: 20

10

0 8 § ~ ~ ~ ~ 8 § ~ ~ ~ ~ 8 ~ i I i N i I i 20 May 1989 21 May 1989

Figure 2 WiJhin storm variation of rainfall pll, precipitation volume and wind direction during Typhoon Brenda.

12 IIKMelS /lULI-ETIN Vol., I, No.1, 1991 pH 5.6 • • • • • • • • •• • c' 5.4 • • • :, •• i! I 5.2 j • • • 5.0 • • • • • 4.8 •

4.6 0 10 20 30 40 50 60 70 Rainfall (rnrn)

Figure 3 Scauergram of rainfall pll against volume ojprecipitation for Typhoon Brenda.

lation between rainfall amount and pH. Never­ therefore, more acidic rainfall are associated with theless, there is some evidence in Figure 2 that, low rainfall rates. However, the low rates of during a storm, rainwater pH may be influenced rainfall at the beginning of the rainfall event did by rainfall amount. For example, pH values not generate low pH values and, moreover, below 5 are confined to rainfall amounts of less rainfall amount may not be the only factor than 20 mm per hour. Comparatively low values causing the low pH values at the end of the of pH were recorded from 0200 hours on May typhoon. 21st. The change from the comparatively high pH values which prevailed before then on May The scattergram of rainfall pH against 21st to the lower levels thereafter coincides with precipitation volume presented for the storm in a significant decrease in rainfall amount. It ap­ Figure 3 evidences no simple association between pears that for this storm low values of pH and, the variables for Typhoon Brenda. However, it llKMetS BULLETIN Vol. 1, No.1, 1991 13 does show that for this event low pH values are might be expected to he relatively clean and non associated with low rainfall. The scattergraph acidic it is somewhat surprising to observe that suggests that other controls over rainfall pH, in the lowest rain water pH is associated with this addition to rainfall volume, may exist. wind direction. As suggested earlier one explana­ tion for this low pH might be that the rainfall Other meteorological factors such as wind derives acidity from the urban area on it's way to direction may control rainwater pH. Figure 2 Kadoorie. A further factor may be that due to the reveals that wind direction changed during approach from the sea, no crustal derived particu­ Typhoon Brenda. In the early hours of sampling late matter is available to buffer the acidity ob­ the wind direction was around 60 degrees. When tained from the urban area. Unfortunately, no the prevailing wind was from this direction its information was collected on the particulate approach to the sampling site was from over the matter content and chemistry of the samples to North East coastal area of Guangdong Province. Iprovide additional information for this hypothe­ By late on May 20th and in the early hours of sis. It should also be remembered that the low May 21st the predominant wind direction had rainfall amount at the end of the storm may also changed to become 110 to 130 degrees. This be responsible for the lower pH values recorded direction of approach opens up Kadoorie to the from 0200 hours onwards on May 21st. Fur­ influence of the urban area of Kowloon and to a thermore, in such a complex circulation as exists lesser extent Tsuen Wan (see Figure I). The in a typhoon it must he recognised that other urban area may provide an increased source of meteorologic factors not considered here may acidity which may explain the lowering of pH at also influence rainwater pH. the end of the storm. The suggestions outl ined above to account The E.P.A. (1985) report that for their for the change in rainfall pH during typhoon monitoring station at Kwun Tong that rainfall pH Brenda indicate that wind direction and meteoro­ related strongly to "crustal deposition fractions" logical factors in general may be of importance in in the sample. They suggest that this particulate explaining within storm variation of pH. Other matter may act to buffer rainwater acidity. This researchers have also noted the importance of may explain the high pH values in rainwater wind direction and meteorological conditions as recorded during the early part of the event, when controls upon rainfall pH (e.g. Camuffo et al. the wind direction was around 60 degrees. During 1984; Skartveit, 1981; Pellet et al. 1981). this part of the storm crustal particulate matter could be obtained from rural areas in NE and E The study of Pellet et al. (1981) is also of Guangdong and parts of the New Territories. interest in that they report results which permit This might act to buffer rainfall pH and could comparison with the present study. They report account for the high pH levels associated with the that rainfall associated with three hurricanes had relatively low rainfall amounts at the start of the rainfall pH which ranged from 5.0 to 5.6. They monitoring period. suggest that high rainfall volume is a factor in these high pH values for their study site near With the wind direction change to Hampton, Virginia. It is interesting to note that 110/130 degrees during the evening of May 20th their results for samples obtained during a hurri­ the direction of approach is from the South China cane are similar to these recorded during Ty­ Sea. Given that moisture derived from the ocean phoon Brenda.

14 IlKMeiS IIULUUIN Vol. I, No.1, 1991 References

BABICH, H., 1980: Acid precipita­ ENVIRONMENTAL PROTECTION ROYAL OBSERVATORY, 1989: tion - causes and consequences. Envi­ DEPARTMENT, 1989: Environment Mo nth ly weath er Summary, May ronment , 22(4), 6-13. Hong Kong, 1989, A Review of 1988. 1989, Royal Observatory, Hong Hong Kong, Government Printer, 219 Kong, l Spp. CAMUFFO, D., M, del MONTE, and pp. A. ONGARO, 1984: The pH of the SKARTVEIT. A., 1981: Relationships atmospheric precipitation in Venice, GORHAM, E., 1976: Acid prcc ipitu­ b ct wc e n precipitation chemistry, related to both the dynamics of precipi­ tion and its influence on aquatic eco­ hydrology and runoff acidity. Hydrol­ tation events and the weathering of systems: An overview. Waler. Air ogy, 12,65-80. monuments. The Science ofthe Total and Soil Poilulion , 6, 457-481. En vironment, 40,125-139. TANG. A.J.S .. WH, CHAN. D.B McCOLL. J.G., L.K. MONETTE and ORR. WS. BARDSWICK and M.A. ENVIRONMENTAL PROTECTION D.S. BUSH 1982: Chemical character­ LUSIS, 1987: An evaluation of the AGEN CY, 1985: Air quality in Hong istics of wet and dry atmospheric precision. and various sources of Kong: res ults from th e E. P.A. air fallout in Northern California. J. error, in daily and cumulative precipi­ qualily monito r ing n et wo rk: for Environ. Qllal. 11(4) 585-591. tation chemistry sampling. Waler, Air 1984/85. Hong Kong, Government and Soil Pollution, 36, 91-102. Printer, 100 pp. PELLETT, G.L.. R. BUSTIN and R,C. HARRIS. 1981: Sequential TANG, C.W. 1981: Acid precipita­ ENVIRONMENTAL PROTECTION sampling and variability of acid precip­ lion - a case study of Kowloon, New DEPARTMENT, 1986: Environment itation in Hampton, Virginia. Waler, Territories and Hong Kong Island. Hong Kong, 1986. Hong Kong, Air and Soil Pollution, 2 I, 33-49. Unpub!. B.A. Dissertation, University Government Printer, 202 pp. o f Hong Kong, 71pp.

flKMelS BULLETIN Vol. 1, No.1, 199/ 15 "yss w: S. Yim Department of Geography & Geology

University ofHong Kong An analysis oftide gauge and storm surge data in Hong Kong *

century by 10-25 em, The best estimate taking ABSTRACT into account the differences in approach of global mean sea level projections by the year 2050 is in the order of 30-70 cm. Sea level rise of this A maximum rate of future sea level rise of ca. 37 magnitude would have disastrous consequences em/century is predicted from an analysis of tide on coastal lowlands including inundation, salini­ gauge data obtained over the past 27 years from zation, and coastal erosion. the North Point (1962-1985) and Quarry Bay (1986-1988) stations in Hong Kong. However, if As shown in Figure 1, at the end of 1984, long term ground-surface settlement of both sta­ 33 sq. km or 3.2 percent of the original area of tions, estimated from surveying data is taken into Hong Kong have been gained through land account, the rate of sea level rise is virtually nil. reclamation from the sea mainly for the purpose A possible explanation for this discrepancy of urban development (Lands Department, 1985). between Hong Kong and the global rate of future Intertidal areas such as Deep Bay which were sea level rise predicted by many overseas workers reclaimed for agriculture are however excluded is the regional subsidence of the Pearl River from this total. The formation level of reclama­ mouth caused by isostatic responses of sedimenta­ tions for urban development is kept as low as tion due to the southerly migration of the Pearl possible for three main reasons: (1) to reduce the River delta. It is therefore recommended that quantities of fill required; (2) to maximize the use long term monitoring of ground-surface settle­ of gravity drainage; (3) to minimize the likeli­ ment of all major land reclamations, as well as all hood of flooding during rainstorms in low-lying operational tide gauge stations in Hong Kong be areas behind seawalls. However, the risk of carried out. inundation resulting from a future rise in sea level is increased if the formation level is kept low.

Introduction The main objective of this paper is to examine the evidence for a future rise in sea level through tide gauge measurements and the histori­ A future rise in sea level is of concern to all cal record of storm surges associated with ty­ forms of coastal development by man. In a phoons in Hong Kong. review by Warwick (1986), global sea level was shown to have risen appreciably over the past Tide Gauge Measurements

• reprinted with additions and alterations from The relative elevation of datums and sea levels in Yim, W.W.S. (Ed.), 1986: Future Sea-level Rise Hong Kong is summarized in Figure 2. Chart and Coastal Development. Abstracts 5, Geol. Datum (C.D.) is used by the Royal Observatory Soc. of Hong Kong and Dept. of Geography & for all sea level observations while Principal Geology, University of Hong Kong, Hong Kong, Datum (P.D.) is adopted by the Crown Lands and 18-26. Survey Office, Hong Kong Government for the

16 HKMelS BUllETIN Vol. I, No.1, 199/ 114'0C1E CHI N A

(J 22'JC1N \ Pearl River Estuary

•, 22"20'N 22"20'N

$ 10k () I m 114'OO'E

Figure 1 Location map oftide gauge stations, reclamations and New Towns in Hong Kong (after Lands Department, 1985).

design of all civil engineering works. The high­ est astronomical tide predicted is 2.7 m P.D., but the maximum sea level during typhoons may

MAXIMUM SEA LEVEL DURING CYCLONE exceed this elevation by more than 3 m. AT TAl PO KAU 1937 The Royal Observatory currently operates nine tide gauge stations in Hong Kong (Cheng, 1986) and these are shown in Figure 1. Hourly readings are obtained and data from some of the stations are telemetered back to the Central Fore­ casting Office on a real-time basis. However, MAXIMUM SEA LEVEL DURING because of breakdown frequencies and difficulties CYCLONE AT NORTH POINT 1937 in maintenance of tide gauge stations located in remote areas, discontinuous records of hourly 6.1m measurements are common. Out of the nine HIGHEST SEA LEVEL FROM stations, North Point, Tai Po Kau and to a lesser TIDE TABLES extent, Chi Ma Wan, possess the most complete record oftide gauge observations. North Point, 3.9m the oldest tide gauge station was operational for 34 years before it was replaced in 1986 by the 2.7m Quarry Bay station about half a kilometre to the east. 1.15m Since the majority of tide gauge stations PRINCIPAL DATUM in Hong Kong have not been operational for a CHART DATUM period of more than twenty years, only three stations with the longest and most continuous record, Chi Ma Wan, North Point and Tai Po Kau, are selected for the present analysis. The periods of tide gauge observations are 1970-1984-, Figure 2 Relative elevations of datums and sea levels in Hong 1962-1988 and 1970-1987 respectively. From Kong (after Yim, 1986). 1986 onwards, tide gauge data of Quarry Bay are used as a continuation of the data from North Point. HKMelS BUlLETIN Vol. 1, No.1, 1991 17 1.7 Chi Ma Wan E ~ ~ ...... North Point "0 t CIS 1.6 ..c ...... Tai Po Kau o Q) > o .0 CIS III ...Q) 1.5 Q) E c: Q) > ~ 1.4 '. CIS -, Q) III -...... c: CIS ...... Q) ...... : :E ...... '" ...... • __ ••••• i 1.3 "'-" ...... ' .....•...... ~ ......

J F M A M J J A s a N o

Month

Figure 3 Comparison of Iti-year monthly mean sea level above chart datum during 1970-1984 at the Chi Ma Wan, North Point and Tai Po Kau tide gauge stations.

A comparison of 15-year monthly mean sea level tion was chosen for the estimation of the rate of during the 1970-1984 period at the three stations future sea level rise for two main reasons. First­ is shown in Figure 3. All of them show a similar ly, this station appears to be the least influenced pattern with the highest monthly mean sea level by coastal configuration and the Coriolis force, in October coinciding with the latter part of the and secondly, it possesses the longest and most typhoon season. Between January and July, the continuous tide gauge record. A plot of the monthly mean sea level is appreciably lower and annual monthly maximum, mean and minimum appears to be related to the dry winter monsoon. sea levels for this station between 1962 and 1988 Chi Ma Wan is found to show the highest month­ is presented in Figure 4. The monthly maximum ly mean sea level followed by Tai Po Kau and followed by the monthly minimum show the North Point. Tai Po Kau shows the greatest greatest fluctuation which may be explained by range of monthly mean sea level (0,323 m) fol­ the changing intensity of the monsoonal effect. lowed by Chi Ma Wan (0.286 m) and North Point Since the monthly mean shows the smallest fluc­ (0.273 m). The difference in range is best ex­ tuation, it is selected for the estimation of the plained by the influence of the coastal configura­ mean rate sea level rise using a graphical method tion on the Coriolis force at each station. Be­ (Figures 4 and 5). Using this method the mean cause of easterly location and the funnel shaped rate of sea level rise during the 1962-1988 period coastline of Chi Ma Wan, the effect of the Corio­ is about 37 em/century which, if continuity of the lis force is at a maximum and the range is in­ trend is assumed is the future rate of sea level termediate. North Point located within Victoria rise. A weak positive correlation of 0.32 exists Harbour which is open to both east and west has, between the annual mean sea level and annual as expected, the lowest range. Tai Po Kau on the precipitation of the Royal Observatory station other hand is located in an easterly oriented semi­ located about 4 km away (Figure 5). Therefore it enclosed harbour and shows the greatest range. is possible that at least part of the rise in sea level may be attributed to a local increase in annual Data for the North Point tide gauge sta­ precipitation.

18 lIKMetS BULLETIN Vol., I, No.1, 1991 1.75 E 1.7 :J .....ro Annual monthly maximum "'0 1.65 Lro ..c 1.6 o Q) > 1.55 0 .0en 1.5 CJ) Mean rate 37 cm / century Q) .....'- 1.45 Q) E .>" -, ____ ~'~'~'~"_":'~-,7",------­ 1.4 Annual mean ..... c / .... ------,--­ Q) 1.35 > Q) \:;~~~~~I- :~;~~:~;:i~:m ro 1.3 Q) I CJ) c 1.25 ro Q) ~ 1.2 1.15 1.1 62 64 66 68 70 72 74 76 78 80 82 84 86 Year Figure 4 Annual monthly maximum, mean and minimum sea levels in metres above chart datum 0/ the North Point tide gauge station during 1962-1986.

1.45 ..------, Ground Surface Settlement --Mean Sea Level i ···------Trend 'tl Because the North Point tide gauge station is ".. '5 t .• located on a seawall overlying soft marine sedi­ ~ ments, long term ground-surface settlement .8.. would introduce error into the measurements. i!! ~ The amount of settlement may be estimated from St.3S a; the surveying record kept by the Port Works ~ Division of the Civil Engineering Services De­ ..:;: partment, Hong Kong Government. Between a.. December 1961 and January 1983, a reference E 1..3 ..::> mark for the tide gauge was found to have fallen ~ in elevation from 4.03 to 3.95 m P.D. by level­ ~ ~ M U 10 n 74 78 78 ~ G ~ 85 M Year ling with an accuracy of 0.01 m. These results 2.500 suggest that during the period of tide gauge --Mean measurements the overall ground-surface settle­ ~ ment was 8 em. Based on this, the adjusted mean rate of sea level rise (Figure 5) is virtually nil. f- However, since the two bench marks used for checking the elevation of the reference f­ mark at the tide gauge station are also on re­ claimed land, at 323 Java Road and 670 King's Road respectively, they are also likely to be af­ fected by long term ground-surface settlement. 1.000 .~ ~ .~ ~ The assumption that these bench marks will L~ ~ 66 ~ 10 n 74 75 78 ~ 82 M M 88 remain unchanged in elevation in time is incorrect Year because they do not have stable foundations. During 1984, two temporary bench marks were Figure 5 Annual trend 0/ mean sea level in metres above chart set up at the North Point and Quarry Bay tide datum of the North Point tide gauge station and annual precipiJa­ gauge stations for surveying purpose. An invest- lion of tire Royal Observatory station during 1962-1988.

HKMetS BUlLETIN Vol. 1, No.1, 1991 19 Table 1 Meteorological observations and maximum sea level ofselected typhoons in Hong Kong since 1937 (based mainly on Chan, 1983).

Maximum sea level in Movement m above chart datum Central Maximum MSL Direction Speed Tropical gust in pressure in in North TaiPo Chi Ma cyclone Year knots in hPa degrees knots Point Kau Wan

Unnamed 1937 130* 949 296 15 4.05 6.25 Mary 1960 103 966* 015 12 2.77 Wanda 1962 140 944* 325 12 3.96 5.03 Ruby 1964 122 954* 303 11 3.14 3.54 3.20 Dot 1964 94 973 360 10 2.65 3.23 2.95 Rose 1971 121 982 360 8 2.56 3.00 2.98 Hope 1979 94 950 260 17 2.78 4.33 2.73 Ellen 1983 128 960 305* 8 3.06 3.06

* Estimated

Table 2 Factors tiffecting storm surge levels (after Lau, 1980).

Parameters of storm Coastal parameters Local factors

central pressure sea floor topography river discharges distance of closest approach coastline configuration seiching translational speed rainfall runoff storm path tidal effects storm size wind effects

igation by the Port Works Division revealed that more, it is desirable to keep a record of any a settlement rate in the order of 5 mm/year is constructional disturbance of their immediate taking place at the seawall and land adjoining the vicinity. Quarry Bay station between 1984 and 1987 (port Works Division, personal communication). However, since the levelling was also based on Storm Surge and Sea Levels the reference bench marks used for the North Point tide gauge station, the true settlement rate is uncertain. A storm surge may be defined as the difference between the observed sea level and the predicted From the above, it is desirable to quantify astronomical tide at the same place and time. the amount of long term ground-surface settle­ During a storm surge, the maximum sea level ment of the tide gauge stations situated on re­ may greatly exceed the predicted astronomical claimed land. In order to improve the quality of tide and threaten low-lying areas of Hong Kong the tide gauge measurements at the Quarry Bay through marine inundation. station, new bench marks located on stable ground would have to be established for future Table 1 provides a summary of meteoro­ surveying exercises. These new bench marks logical observations and maximum sea level of should be located further inland of the existing selected typhoons in Hong Kong since 1937 after ones on structures founded on bedrock. Further­ Chan (1983). Tai Po Kau is found to show con-

20 HKMetS BUUETIN Vol. 1, No.1, 1991 110'E

CHI N A 79--­3 7

SOU T H CHINA SEA I °pARACEL • ISLANDS

I----->,.---t------t------t----:~__+------+ IS'N

Figure 6 Tropical cyclone tracks responsible for maximum storm surge levels in Hong Kong (after Peterson, 1975).

sistently the highest maximum sea level followed by Chi Ma Wan and North Point. Generally, the Table 3 Return periods ofmaximum sea level in metres above highest maximum sea levels found at all stations C.D. estimated using Gumbel's method (after Chan, 1983). were associated with the highest maximum gust, the lowest central mean sea level pressure and a west-northwesterly direction of cyclone move­ Return Station ment at the greatest speed. Out of the factors Period influencing storm surge levels (Table 2), coastline configuration, cyclone path and speed appear to (in yr) North Point Tai Po Kau Chi Ma Wan be mainly responsible for causing the highest 1950-1981 1962-1981 1963-1981 maximum sea level. The maximum sea level of 6.25 m C.D. recorded at Tai Po Kau in 1937 was caused by the semi-enclosed nature of Tolo 10 3.34 4.13 3.40 Harbour which is conducive to extreme seiching. Furthermore, storm surges were found to be the 50 3.71 5.01 3.74 most pronounced when the centre of a typhoon moving westward passes over Hong Kong direct­ 100 3.86 5.39 3.89 ly or within 13 km to the south (Watts, 1959). These typhoons have typically almost straight 200 4.01 5.76 4.03 west-north-westerly courses through the strait between Taiwan and Luzon (Figure 6). 500 4.22 6.25 4.22

A statistical method was used by Peterson (1975) 1000 4.37 6.62 4.37 to estimate the return periods of sea levels by combining the effects of storm surges and astro­ nomical tides. However, Chan (1983) considered that interactions between storm surges and astro­ nomical tides may lead to uncertainties in the annual maximum sea levels were extracted from results. Instead, the method of Gumbel (1954) monthly maximum hourly sea levels, it is possible was adopted by Chan (1983) and applied to data that higher sea levels may have occurred. Thc.» on annual maximum sea levels for estimation of fore the return periods for various specified sea return periods (Table 3). In the case of Tai Po levels at Tai Po Kau and Chi Ma Wan are likely Kau and Chi Ma Wan, because some of the to be less than pred icted.

IIKMetS BUllETIN Vol. I, No. I, 1991 21 A future sea level rise may threaten Hong not been located on stable ground. As a result of Kong in two ways. firstly, a gradual increase in these uncertainties, it is proposed that long term mean sea level, and an increase in the frequency monitoring of ground-surface settlement should of typhoons associated with storm surges. be carried out in all major land reclamations in However, both are difficult to predict given the Hong Kong. The information obtained would short meteorological record available. This is indirectly benefit storm surge analysis for coastal further complicated by the appearance of EI Nino engineering through an improvement in quality of years during which the global climatic pattern is tide gauge data. If the discrepancy between mean known to change drastically. For example, EI sea level trends found for Hong Kong and other Nino years appear to be associated with a decline parts of the world is real, then local subsidence of in typhoon activity influencing Hong Kong. the crust in response to sedimentation of the Pearl After the termination of an EI Nino episode, their River during modern times is a probable explana­ resurgence may be expected. tion. Research work on this topic would be helpful to assist the future coastal development of Hong Kong. Conclusions Acknowledgements The mean rate of future sea level rise obtained by extrapolation of annual mean sea level at the North Point tide gauge station during 1962 - 1988 I am particularly grateful to the Chief Engineer of is about 37 em per century. If ground-surface the Port Works Division, Civil Engineering settlement is taken into account, the mean rate Services Department, Hong Kong Government, which does not take into consideration the in­ and the Director, Royal Observatory, Hong Kong creasing input of carbon dioxide into the atmos­ for the provision of data. All opinions expressed phere and the greenhouse effect is virtually nil. in this paper are entirely my responsibility. I However, there are uncertainties in the estimation would also like to thank M.L. Chalmers, D.R. of the amount and rate of ground-surface settle­ Workman and staff members of the Port Works ment because either the tide gauge station or the Division for their constructive criticisms. bench marks used for checking its elevation have

22 llKMetS BUllETIN Vol. 1, No.1, 1991 References

CHAN, Y.K., 1983: Statistics of LANDS DEPARTMENT, 1985: WATTS, I.E.M., 1959: The effect of extreme sea levels in Hong Kong. Reclamation and Development in Hong meteorological conditions on tide Tech. Note (Local), 35, Royal Ob­ Kong. Hong Kong Government. height in Hong Kong. Tech. Memoir, servatory, Hong Kong, 28 pp. 8, Royal Observatory, Hong Kong, LAU, R., 1980: Storm surge investiga­ 30pp. CHENG, T.S., 1986: Sea level related tions and the use ofvertically integrat­ studies at the Royal Observatory, ed hydrodynamical models. Tech. YIM, W.W.S., 1986: A sea level Hong Kong. in W.W.S. Vim, (Ed.), Note 53, Royal Observatory, Hong curve for Hong Kong during the last Sea level changes in Hong Kong Kong, 42 pp. 40,000 years. in w.W.S. Vim (Ed.), during the last 40,()()() years. Abstract Sea level changes in Hong Kong 3, Geo!. Soc. of Hong Kong and Dept. PETERSON, P., 1975: Storm surge during the last 40,()()() years. Abstracts of Geog. & Geo!., University of Hong statistics. Tech. Note (Local), 20, 3, Geo!. Soc. of Hong Kong and Dept. Kong, 34-36. Royal Observatory, Hong Kong, 18 of Geog. & Geo!., University of Hong pp. Kong, 23-30. GUMBEL, E.]., 1954: Statistical Theory of Extreme Values and Some WARWICK, R.A., 1986: Climatic Practical Applications. U.S. Dept. of change and sea level rise. Climate Commerce, Washington, D.C. Monitor, 15, 39-44.

HKMetS BUlLETIN Vol. I, No.1, 1991 23 News and Announcements

This section is intended for dissemination of news and Date: 24 June, 1990 announcements by the Society or any ofits members. If members wish to relay any news or make any announcement THE THREAT OF THE GREENHOUSE ofinterest to members which is related 10 the aims ofthe EFFECT Society they should mail or fax such information to the by Dr. C.N. Ng, City Polytechnic of Hong Kong Editor-in-chief along with their name(s) and membership number(s). Date: 1 July, 1990

URBAN MICROCLIMATE by Dr. W.L. Chang, Royal Observatory, PUBLIC LECTURE SERIES Hong Kong

Date: 8 July, 1990 The Hong Kong Space Museum and the Hong Kong Meteorological Society (HKMetS) have NEW WEATHER EYES AND EARS jointly organized a successful series of public by Mr. Edwin S.T. Lai, Royal Observatory, lectures in Cantonese planned with a view to Hong Kong improving the meteorological interest and knowl­ edge of Hong Kong citizens. The series ran from The popularity of the series has prompted 3 June to 8 July 1990 and was well attended. The requests from the Hong Kong Space Museum for subjects of the lectures and the guest speakers, all another series to be run in 1991. The Committee of whom are members of the Society are listed has supported this request and encourages below. members who are interested in providing the benefits of their experience to the public in this Date: 3 June, 1990 way to contact the Hon. Secretary for details.

TROPICAL CYCLONES - A CASE FOR THE DEFENCE HONG KONG IS OUR HOME ­ by Dr. Johnny Chan, City Polytechnic of Hong Kong EXHIBITION ON LIVING IN THE GLOBAL GREENHOUSE 90 Date: 10 June, 1990

HEAVY RAIN AND LANDSLIDES The Hong Kong Association for the Advancement by Mr. R.K.S. Chan, Geotechnical Control of Science and Technology (HKAAST) and the Office, Hong Kong Government Hong Kong Meteorological Society (HKMetS) have jointly organized a successful travelling Date: 17 June, 1990 exhibition planned with a view to improving the environmental awareness of Hong Kong citizens EL NINO AND UNUSUAL WEATHER and schoolchildren. The exhibition, which took by Mr. W.C. Lee, Royal Observatory the form of panelled displays ran from 14 Sep­ Hong Kong tember to 14 October 1990 and was seen by an estimated 100,000 people. Its objective was to

24 HKMetS BULLETIN Vol. 1, No.1, 1991 increase the awareness of the general public, and to Shun Tak Shopping Mall in Central on 21 secondary and tertiary students in particular, September. On 24 September it moved again to concerning the problems associated with potential CMA Choi Cheung Kok Prevocational School in global warming. It also focussed on the action Tuen Mun and then to Lok Fu Shopping Centre, that can be taken to assist humanity to adjust to Lok Fu Estate, Kowloon on 28 September. On 1 the reality that what they do as individuals is October the 6th show opened at TWGHs Wong important and relevant to providing acceptable Fut Nam College, Kowloon Tong. The next solutions to the issues which confront society show opened on 4 October at City Plaza, Taikoo regarding the question of present policy and Shing. From there it was transferred to Cheung future climate. ·Chuk Shan College, North Point on 8 October and finally to New Town Plaza in Shatin on 12 The display materials were a comprehensive October for the 12th and last show. range of pictures with bilingual captions describ­ ing the natural and man-made causes of climatic As a Society one of the aims of the HKMetS is changes, the greenhouse effect, depletion of the to help increase people's knowledge of both the ozone layer, adverse effects of atmospheric atmosphere and the measures that can be taken to change, as well as international scientific pro­ reduce the adverse effects of human activity on grammes for monitoring the atmosphere. On site the climate. Sponsoring the Exhibition was a presentations were conducted by specially trained useful way of promoting our interests in this area. University and Polytechnic students at each of the The objective of the event was to try to get across venues. to the general public that our use of energy, our lifestyles and so on, are affecting the atmosphere The Opening Ceremony was held at the Hong of the planet as a whole and that it is a serious Kong Cultural Centre on 14 September, 1990 problem which has global implications. The idea with the Hon. Graham Barnes, CBE, JP, Secre­ was also promoted that individuals can do their tary for Planning, Environment and Lands, kindly bit to help even if it is only a small contribution officiating. The Show then remained at the to the overall solution of the problem. This was Cultural Centre until 17 September when it in keeping with the motto "Think Globally Act moved to NT Heung Yee Kuk Taipo District Locally" . Secondary School. From there it was transferred

2S HKMetS BULLETIN Vol. 1, No.1, 1991 Correspondence

This section is an open forum where members may voice or In April 1990, a global warming confer­ exchange views or opinions on any subject related to the ence was held in Washington, D. C. under the aims ofthe Society. Members are encouraged to submit such auspices of the White House. A cynic might say views to the Editor-in-chief either by mail or by fax with the that the U.S. Administration hoped to orchestrate only limitation being that to be published such communica­ a debate on the uncertainties of the greenhouse tions are of resonable length and are accompanied by the effect. However, most delegates appeared to name(s) and membership number(s) ofthe submitterts). The agree that global warming is a real, potentially Editor-in-chief reserves the right to edit any submission due serious threat. There was consensus that un­ to space limitations or to conform to established style but checked accumulation of greenhouse gases will will only publish such edited material with the prior agree­ lead to warming but there was great uncertainty ment of the submitter(s). All opinions expressed in such as to when, by how much, and how rapidly it will correspondence are those ofthe author(s) and do not neces­ occur. sarily reflect those ofthe Society. This result illustrates clearly the dilemma we face: how to set policy based on uncertain predictions of the future. The most widely ac­ OUT OF THE FRYING PAN ..... cepted estimates of global warming are from 1.5 to 4.5 °C as early as 2050. Yet the computer As concerned scientists we are all aware models used to make the projections may not that the Earth is threatened by a multitude of accurately incorporate such factors as the role of manmade hazards from coastal pollution to the clouds and the capacity of the oceans to absorb depletion of the Antarctic ozone layer. Recently, heat. however, one aspect of these symptoms of ill health, the theory that the build-up of carbon Despite the uncertainties, there is a broad dioxide and other greenhouse gases such as consensus that we should slow down the rate at CFC's, methane and nitrogen oxides, will cause which we are altering the atmosphere. Yet there global warming has been challenged by a small is also concern about the economic and political but vocal group. They contend that the case for consequences of major shifts in energy use poli­ warming is weak and based on inadequate com­ cy. Is it possible to spur energy conservation so puter models. long as the scientific evidence is incomplete? Can we buy insurance against global warming Not surprisingly, some politicians have without sabotaging the world economy? What do coveted this opportunity to caution against undue you think and what should be the role of Hong haste in making decisions. In the U.S. substantial Kong scientists, educators and policymakers in influence has been brought to bear on the Admin­ this important issue? istration. Only recently, for example, President Bush, while not dismissing the potential threat, has emphasized the need for more scientific Bill Kyle research to help determine the proper policy Climatologist response. This slowdown has irritated some, University of Hong Kong particularly in Western Europe.

26 HKMetS BULLETIN Vol. 1, No.1, 1991 Bill Kyle Department ofGeography & Geology University ofHong Kong

Hong Kong Weather Reviews

Climatological information employed in the compilation of with long hours of sunshine. During the first this section is derived from published weather data of the week temperatures climbed steadily and the Royal Observatory, Hong Kong and is used with the prior maximum temperature of 23.3 °C recorded on 7th permission ofthe Director. was the highest for the month. Under stable conditions haze occurred several times from 5th to 9th and from 14th to 16th. Fresh easterly winds developed on 17th and the weather deterio­ Review ofwinter 1989-90 rated the following day. From 18th onwards an extensive area of cloud and rain affected southern Important climatological events China. Locally, some light rain fell during the night of 18th and 19th. Active upper air disturb­ Winter 1989-90, with just over 300 ances then moved in from the west bringing rain percent of normal rainfall for the three month which became heavier and more persistent in the period, witnessed a return to wetter conditions evening of 22nd and remained until 25th when it after six consecutive drier than normal eased off in the morning, though the weather months. Although all three months were remained rather cool. A minimum temperature wetter than normal February was particularly of 13.1 °C on 24th, repeated on 27th, was the wet. It was the fifth wettest February on lowest recorded for the month. The 28th was a record with 467 percent of normal rainfall. much brighter day but cloudy weather returned December marked the transition with the first on 29th following the passage of a weak cold half having clear skies and brilliant sunshine front. Light rain occurred on the following two while the latter part was cloudy and rainy. mornings and heavier rain then persisted till the January was generally cloudy and humid, end of the month. following which February was even wetter and more humid. Mean daily temperature 17.8°C (+0.1°C) Rainfall (provisional) 40.2 mm (159 %) Mean daily temperature 16.6°C (+ 0.2°C) Rainfall (provisional) 283.4 mm (301 %) January December January was generally cloudy and humid with more rain than normal. The monthly mean There was a marked contrast between the relative humidity was the eighth highest on re­ first half of the month which was clear and sunny cord. There were only seven days with no rain and the latter which was cloudy and rainy. Two recorded at the Royal Observatory during the major rain episodes occurred, one before Christ­ month and the total rainfall was 77 percent above mas and the other before the New Year to give normal for the month. total rainfall 59 percent above average for the month. The New Year began with light rain on the morning of l st , with more falling on the For the first seventeen days southern morning of 2nd as northerly winds freshened. China was dominated by dry continental air. The There was no rain for the next two days but nights were generally cool but days were mild cloudy, cool conditions continued as fresh easter­

HKMetS BULLETIN Vol. I, No. I, 1991 27

------Daily maximum temperature trends Daily mean temperature trends

Temperature (C) 21 ~~====:-'--'------21,-'---""---'--'------,

19 19

17 17

15 15

13 13 December January February Winter December January February Winler Winter 1989-90 Winter 1989/90

I- Maximum II>\\\'J Nanna. Maximum' I- Mean I1i\\\'J Nanna! Mean I

Daily minimum temperature trends Rainfall trends

Temperature (C) Rainfall (mm) 21,-"------'-'------, 300,-----'-----'------,

250

200

17 150

100 15 50

13 December January February Winter Winter 1989/90 Winter 1989/90

I- Minimum I1i\\\'J Nannal Minimum I I- Tatal Ramfall II>\\\'J Nanna. Rainfall I lies replaced the northerlies. Some drizzle fell on 28th with rain increasing over the next two days the nights of 5th and 6th although there were as winds freshened from the east. An intense periods of sunshine during the day. The clouds surge of the winter monsoon crossed the coast on broke on 7th and fine weather remained till 12th. the night of 30th bringing light rain and even Although easterlies occasionally freshened, rela­ colder weather with temperatures at the Royal tively warm conditions persisted with the maxi­ Observatory dropping by more than 8 °C within mum of 22.1 °C on 10th being the warmest 24 hours. By the evening of 31st the temperature recorded for the month. At times the freshening had fallen to 8°C, the lowest for the month and easterlies mixed with moist air from the south to the coldest of the winter to that time. give mist and fog offshore. An approaching trough, and the associated clouds, ended the fine Mean daily temperature lSo9"C (+003°C) spell on 13th. From then on conditions were Rainfall (provisional) 47.s mm (177 %) dominated by the winter monsoon with general cloudiness and light rain occurring mainly at night and in the morning. A cold front passed on February 15th bringing strong northerly winds and light rain. This was followed on the 19th by another February was even wetter and more replenishment bringing more rain and a further humid than January, with the month having the lowering of temperatures. A more intense surge sixth highest relative humidity and fifth highest occurred early on 22nd causing temperatures to rainfall on record. The monthly rainfall was fall below 10°C for the first time in the winter on more than four and a hal f times the normal the morning of 23rd. The northerlies were re­ February figure. placed by fresh easterlies on 24th. Temperatures rose gradually over the next few days with no The intense cold surge at the end of further cold surges. A brief lull in the easterlies January reached its climax early on 1st when on Chinese New Year's Day, 27th, resulted in a temperatures at the Royal Observatory dropped to fine day. This was the only rain free period in a a low of 7°C, the lowest for the month and the long spell of dull weather. Clouds returned on coldest of the winter. Temperatures dropped to 4

28 HKMetS BULLETIN Vol. 1, No.1, 1991 or 5 °C over the New Territories and reached although the month was considerably cooler near freezing over high ground. Easterlies re­ and drier than normal with just over one third placed northerlies later on 1st, and some sunny of normal rainfall and mean daily air tempera­ periods on 2nd caused temperatures to climb ture 1.3 °C below normal. slowly. A weak replenishment brought them down again on 4th. From 5th to 22nd, a mainly Mean daily temperature 21.7°C (-0.7°C) easterly regime prevailed apart from a brief Rainfall (provisional) 389.9 mm (79 %) northerly episode on 11th. The weather from 5th to 15th was variable with periods of sunshine and some light rain. Conditions were misty at times March when warm, moist air from the Pacific reached coastal areas on the mornings of 9th and 12th. While the first two months of 1990 were One of the two warmest days of the month oc­ wet and humid, March was drier and brighter. curred on 14th when a maximum of 23.4 °C was The monthly rainfall was 45 percent below recorded. Outbreaks of rain and the first thunder normal but bright sunshine was 20 percent above of the year was heard as upper atmospheric dis­ normal due to the persistence of a continental turbances affected the coastal area early on 16th. anticyclone over China for most of the month. I More thunderstorms developed and the rain got The monthly mean pressure was the fifth highest heavier on 17th. Winds dropped on 19th and recorded for the month reflecting the dominance there was a break from overcast rainy conditions of the winter monsoon circulation. resulting in the same maximum temperature as on 14th. However, freshening easterlies on 20th The first few days were affected by the brought the rain back to persist for two more persistence of the frontal clouds associated with days. Squalls, associated with thunderstorms, the cold northerly surge at the end of February were particularly severe on the night of 22nd. leading to drizzle and light rain which became Fog in inshore waters was also common during less frequent by 4th. However, the temperature this period. An intense cold surge terminated the continued to drop as cold air was replenished easterly regime on 23rd with the passage of the from the north producing the lowest minimum associated cold front bringing thunderstorms in temperature of 10.8 °C for the month on the the afternoon. For the next few days, dull condi­ morning of 5th. The establishment of dry conti­ tions with persistent rain prevailed with tempera­ nental air cleared away the clouds giving sunny tures dropping below 10°C on the mornings of periods on 5th and 6th although light rain oc­ 25th and 26th. Easterlies strengthened again curred on the evening of 6th. Winds turned early on 27th but soon gave way to a northerly easterly giving mainly fine weather with coastal replenishment later that evening. Although cold, mist on 7th and 8th. However, as moisture overcast weather continued to the end of the increased in the lower atmosphere cloudier month, the rain eased off. weather returned on 9th although there were long periods of sunshine during the next few days. Mean daily temperature 16.2°C (+0.3°C) Visibility deteriorated on the night of 11th with Rainfall (provisional) 195.7 mm (467 %) persistent fog offshore and in the harbour in the morning of 12th. Easterlies freshened on 13th producing cloudy weather till 16th when there Review ofspring 1990 was some morning rain. Weather then turned generally fine until 22nd except for a brief cloudy Important climatological events spell on 18th. The winter monsoon was relative­ ly inactive for the rest of the month apart from two easterly flows which occurred on 26th and Spring 1990 was generally cool and dry 30th. Prior to the first, weather was warm and overall with just over three quarters of the humid with bright periods during the day and normal rainfall for the three month period. light drizzle morning and evening. Coastal mist March and May were much drier than normal patches were prevalent with the worst visibility in but this was partly offset by a wet April with inshore areas on the morning of 24th. The next rainfall 85 percent above normal. The season day was the warmest of the month with a maxi­ started off with a dry and bright March with mum temperature of 27.8 "C. Cloud with light normal temperatures in marked contrast to the rain returned over the next two days followed by wet and humid first two months of the year. some bright periods on 28th. However, rain However, April saw the return of gloomy, wet clouds and thunderstorms which developed over conditions with below normal temperatures western Guangdong and drifted east affected the which persisted for most of the month. May territory giving unsettled weather for the remain­ continued the brighter conditions of late April der of the month with the heaviest rainfall of 23.4

HKMetS BULLETIN Vol. 1, No.1, 1991 29 r j \ I

Daily maximum temperature trends Daily mean temperature trends

30 ;.::.T.=m!:.:p.::.:ra=tu::.:r.:.-c(::..:.C)~ ---, Temperalure (c) 30 ,----~----'.------,

26 26

26

22

20

16

16 16 March April M.y Spring March April M.y Spring Spring 1990 Spring 1990

I- Maximum ~ Normal Maximum I- M••n ~ Norm.1 M••n

Daily minimum temperature trends Rainfall trends

30 ,:..:T.:.=m"-p.:::...r.---'tu=-r.:....:(c::.:C)~ _ Rainrall (mm) 600,---'-----'------,

26 500 26 400 2,4. 300 22 200 20

16 100

16 ~--="--- March April M.y Spring April M.y Spring 1990 Spring 1990

( _ Minimum ~ Norm.1 Minimum ~ I I- Tot.1 R.inf.ll Norm.l Rainf.ll I mm on 30th. Mist and coastal fog persisted Later on 8th the easterlies freshened and condi­ during this period. . tions became increasingly unsettled over the next few days as upper air disturbances became active. Mean daily temperature 18.5°C ( O.O°C) These brought squally thunderstorms which were Rainfall (provisional) 29.9 mm (55 %) most severe on the morning of 11th with gusts of hurricane force being recorded at Waglan Island. Conditions improved on 12th and 13th as a weak: April northerly airstream affected coastal areas but cloudy conditions returned on 14th with light rain In contrast to March, April was cool, dull becoming more frequent over the next two days. and wet for most of the month. The duration of Strong easterlies early on 17th gave cooler sunshine, 73.8 hours, was the 10th lowest on weather but as they moderated encroachment of record and there were only three days when no moist maritime air produced near saturated, rainfall was recorded at Royal Observatory. extremely humid and misty conditions with per­ Monthly total rainfall was 85 percent above sistent sea fog offshore on 19th and 20th. Gusty normal and mean daily air temperature was 0.7 southwesterlies appeared on 21st and with periods °C below normal. of sunshine appearing the next day, the tempera­ ture reached a maximum for the month of 29.3 The first few days of the month were "C. Easterlies strengthened again on 23rd with cloudy due to a trough of low pressure over outbreaks of rain and thunderstorms that evening. Guangdong. Weather deteriorated on the evening Light, continuous rain continued through the of 3rd as a cold front approached from the north. following day becoming heavier on 25th, finally Its passage brought periods of heavy rain and ending on the morning of 26th. As easterlies thunderstorms which eased during 4th although a moderated and a ridge of high pressure became cool northerly airstream resulted in the lowest established over southeast China sunny periods minimum temperature of 16.9 °C being recorded developed during the last few days although fog on the morning of 5th. Winds turned easterly and patches returned on the morning of 30th. For the moderated giving brighter periods on 6th and 7th. second time in the month the maximum tempera-

30 HKMetS BULLETIN Vol. 1, No.1, 1991 ture reached the high of 29.3 °C on that day. highest for the month.

Mean daily temperature 21.4°C (-0.7°C) Mean daily temperature 24.6°C (-1.3°C) Rainfall (provisional) 257.6 mm (185 %) Rainfall (provisional) 102.4 mm (34 %)

May Review of summer 1990 A wet April was followed by a very dry Important climatological events May with monthly rainfall just over one third of the normal of 298.1 mm. The month was also markedly cool with mean daily air temperature Like spring before it summer 1990 was 1.3 °C below normal. relatively dry with about three quarters of normal rainfall. The season started off with close to The sunny weather at the end of April normal temperatures and rainfall in June. July continued into early May although visibility was was somewhat drier with only 85 percent of often poor in the mornings and evenings of the normal rain but August was exceptionally dry I first three days. Cloudiness and intermittent light and hot with just over one third of normal I rain occurred on 4th following passage of a weak rainfall and record high temperatures for the trough the previous night. The advection of month. cooler air produced a minimum temperature of 19.9 °C on the morning of 5th, the lowest for the Mean daily temperature 29.1°C (+ 0.6°C) month. After moderation of the northerlies, Rainfall (provisional) 866.2 mm (75 %) bright and calm conditions prevailed over the next few days until a moist easterly airstream developed on the night of 8th bringing a return of June cloudy conditions. Scattered thunderstorms occurred on the morning of 9th ushering an unset­ In sharp contrast to May, June was a tled period when rain clouds developed from an month characterized by near normal conditions area of low pressure near Beibu Wan and passed with rainfall only 4 percent above normal and eastwards over Hong Kong. Rain was heaviest mean daily temperature 0.2 °C above normal. on 11th and another outbreak on the night of 12th Circulation patterns were also not unusual with was accompanied by some thunderstorms. The most of the rainfall related to the passage of rain eased on 13th and long sunny periods oc­ troughs and unstable airstreams associated with curred on 14th but freshening easterlies on that tropical cyclones. night brought back clouds and some morning and evening drizzle on 15th and 16th. Rain became The month started with heavy downpours heavier later on 17th with the passage of a accompanied by squally thunderstorms ahead of trough, the northerlies behind it bringing relative­ and during the passage of a trough. Over 100 ly cooler weather. During this time Marian mm fell during a 2-hour period around noon on developed into a tropical storm near Nansha and 1st. The rain gradually eased over the next two intensified to a typhoon while moving north days but a fresh easterly airstream maintained towards Xisha. This necessitated the hoisting of cloudy conditions and brought slightly cooler tropical cyclone signals for the first time in 1990 weather. The minimum temperature of 23°C on on 17th. Conditions were mainly cloudy with 3rd was the lowest recorded for the month. After strong offshore winds as Marian turned north­ the easterlies moderated on 3rd the weather from eastwards and headed towards Dongsha on 18th. 4th to 7th was a mixture of brief sunshine and As Marian moved away in the direction of passing showers. Unsettled weather returned on Taiwan, drier air from the continent returned 8th with occasional thunderstorms associated with giving sunny, generally fine weather for the next the passage of another trough in the evening. four days. With the passage of a trough early on Easterlies then freshened and rainy weather with 24th, the weather turned cloudy and relatively isolated thunderstorms persisted till the morning cool. Light rain became nearly continuous from of 11th. After this the easterlies subsided and the the evening of 25th to the afternoon of 27th. A weather improved becoming generally fine for the lull in the easterlies gave a brighter day on 28th next four days. The easterlies freshened again on but winds freshened again the next day and the night of 15th as an area of low pressure west clouds returned. After some morning rain on of Luzon developed into tropical depression 30th, the easterlies subsided and brighter weather Nathan. This strengthened and tracked towards returned. Sunny skies on 31 st ended the month Xisha early on 16th before turning northwestward with a maximum temperature of 30.7 °C, the later on 17th before crossing Leizhou Peninsula

HKMetS BULLETIN Vol. 1, No.1, 1991 31 Daily maximum temperature trends Daily mean temperature trends

Temperature (C) Temperature (C) 33 ~~----'---'------, 33,----"'------'--'------,

31 31

29

27

25 June July Au&usl Summer June July AugulIlt Summer Summer 1990 Summer 1990

Maximum ~ Normal MoxUnum ~ I- I- Mean Normal Mean I

Daily minimum temperature trends Rainfall trends

Temperature (C) Rainfall (mm) 33,-----'-----'--'------, 1200 ~--'------'------,

1000 31 600

29 600

400 27 200

25 June July August Summer June July August Summer Summer 1990 Summer 1990 ~ ~ I- MinUnum Normal Minimum I I- Tolal Rainfall Normal Rainfall I on 18th. During this time disturbed weather July along the periphery of Nathan I s circulation brought windy conditions and squally showers. July was a warm, dry month with both Sunny and hot weather returned on 19th as the mean temperature and the mean minimum Nathan dissipated over Guangxi. The fine spell temperature the seventh highest on record, and a was interrupted by a hazy day on 22nd due to mean relative humidity of 79 percent, the ninth northwesterly winds followed by a cloudy day lowest on record. The monthly rainfall total was before fine weather returned on 24th. During the 15 percent below normal since the weather was next three days, showers occurred in early basically fine except for showers associated with morning, the heaviest on 26th being accompanied an unstable westerly airstream in mid-month and by thunder and lightning. However, these had periods of rain brought by STS Tasha towards the little effect on daytime heating and the maximum end of the month. temperature for the month of 32.9 °C was record­ ed on 27th. Cloud returned on 29th as Typhoon The month started cloudy in the aftermath Percy approached the southeast China coast with of Typhoon Percy but brightened the following an outer rainband bringing some showers that day. A ridge of high pressure extended west­ morning. Heavier rain did not occur till the next wards from the Ryuku Islands to produce fine hot day as Percy moved further inland and an unsta­ weather apart from a some brief showers over the ble southwesterly airstream affected coastal areas. next few days giving rise to a maximum tempera­ Intense rain clouds developed frequently over the ture for the month of 33.3 °C on 5th. Heavier Pearl River Estuary and moved in sequence showers occurred on the morning of 6th but the across Hong Kong bringing periods of heavy rain fine spell returned and continued to 11th when and thunderstorms to end the month. active southwest monsoon brought increasingly unsettled conditions culminating in showers and Mean daily temperature 27.9"C (+ 0.2°C) thunderstorms in the morning and evening of Rainfall (provisional) 448.1 mm (104 %) 12th. This unsettled spell continued to 15th when a ridge extending from the Pacific reinstated the fine weather for a further five days. Coastal

32 HKMetS BULLETIN Vol. 1, No.1, 1991 areas then came under the influence of an easterly and hazy on the 17th. The temperature stayed airstream from 21st to 23rd as an area of low above 30°C that night and as heat built up the pressure moved west across the South China Sea. following day all was set for the record breaking Although weather remained basically fine some conditions of 18th. With the approach of Yancy thunderstorms occurred during this time. The to the coast of Fujian between 20th and 22nd easterlies moderated and after heavy rain early on cloudy weather spread across the coastal areas. 24th the weather improved to give sunny, rainfree These broke on 23rd although as the remains of days on 25th and 26th before intense daytime Yancy moved west along the coast some light heating produced thunderstorms again on 27th. rain occurred that evening. Fine weather then The last few days were dominated by the prevailed for three days apart from light showers presence of tropical storm Tasha to the east of on the morning of 25th. For the next four days Hong Kong. Weather became increasingly the weather was influenced by Typhoon Becky cloudy on 28th and 29th and as Tasha approached which moved westwards across the South China the coast of eastern Guangdong on 30th the Sea. Clouds increased as the easterlies freshened weather deteriorated further with periods of on 27th. Winds increased the next day bringing squally rain and strong northerly winds. After squally showers. Both eased off on 29th as landfall on 31st the winds moderated but squally, Becky passed to the south of Hainan before dissi­ thundery showers persisted during which the pating over Vietnam. Fine conditions then re­ I monthly minimum temperature of 23.8 °C was turned for the remainder of the month. recorded. Mean daily temperature 29.5°C (+ 1.3°C) Mean daily temperature 29.0°C (+0.4°C) Rainfall (provisional) 150.1 mm (36 %) Rainfall (provisional) 268.0 mm (85 %) Review ofautumn 1990 August Important climatological events August was exceptional in being the hottest and driest on record in Hong Kong. On After a dry summer, autumn 1990 was 18th the temperature reached 36.1 DC, equalling 15 percent wetter than normal, although this the high set 90 years ago. The mean temperature was principally due to a wet September since of 31.9°C, and minimum temperature of 30. 1 °C October was drier than normal and November recorded on that day made it the hottest on re­ rainfall was near normal. The season was also cord. The monthly mean temperature of 29.5 °C warmer than normal with November being and monthly mean minimum temperature of 27.4 considerably warmer despite a high incidence °C are also record highs and the monthly mean of winter monsoon circulation. maximum temperature of 32.1 °C is the second highest ever recorded. The monthly mean rela­ Mean daily temperature 25.0°C (+ 0.4°C) tive humidity of 75 percent is also the lowest ever Rainfall (provisional) 547.5 mm (115 %) recorded for August. With such a hot, dry month rainfall was also low, the total of 150.1 mm being the tenth lowest on record and only 36 percent of September normal for the month. Overall, September was warm but rela­ The month started cloudy and unsettled in tively cloudy and wet with monthly rainfall being the moist southwesterly airstream in the wake of 28 percent above normal. Over half of the STS Tasha. The first three days registered 100 month's rain could be attributed to the passage of mm of rain, two thirds of the total for the month. Typhoon Dot across southern China. Over the next three days fine, hot weather gradu­ ally became established to set the pattern for the The first two days were sunny and very month. There were outbreaks of thunderstorm hot with the passage of Typhoon Abe over eastern activity on 11th and 13th and passage of a major China bringing a continental air mass to the south squall line caused the temperature to drop to a China coastal areas. On 2nd relative humidity low of 25°C for the month on 16th. For the next dropped below 50 percent and temperature six days Hong Kong came under the influence of reached a maximum of 33.8 °C for the month. Typhoon Yancy in the western North Pacific Winds then turned easterly giving some light Ocean. This initially brought relatively dry showers but generally fine weather persisted till continental air in the northwesterly circulation an outbreak of thunderstorms in the afternoon of which affected the territory. Conditions were 6th. Hong Kong then came under the influence fine during the initial part of this period being hot of Typhoon Dot which crossed Taiwan on the

HKMetS BULLETIN Vol. 1, No.1, 1991 33 Daily maximum temperature trends Daily mean temperature trends

;.:.Te=m~pec:...:ra:.:..:tu:.:..:re,--,(:.:..:C) Temperature (C) 32 -----, 32

30 30

28 28

26 28 24

22 22

20 20

18 18 September Oet..ober November Aulwnn September October November Autumn Autumn 1990 Autumn 1990 ~ ~ I ­ Maximum Nonna! Maximum I I ­ Mean Nonna! Mean I

Daily minimum temperature trends Rainfall trends

Temperature (C) Rainfall (mm) 32 600,------,

30 500 28 400 26 300 24 200 22

20 100

18 September October November Autumn September October November Autumn Autumn 1990 Autumn 1990 ~ ~ I- Minimum Nonnal Minimum I I- Total Rainfall Nonnal Rainfall I night of 7th and passed over the Taiwan Strait the next day making landfall near Xiamen. Weather October was fine on 7th but the typhoon brought torrential rainfall over the next five days as it degenerated October was about 10 percent sunnier over southern China. Rainfall exceeded 230 mm than normal and also had the seventh highest over the 5-day period from 8th to 12th, being mean monthly atmospheric pressure on record heaviest on 10th when over 100 mm were record­ both reflecting the dominance of the continental ed. Conditions improved on 13th with generally anticyclone in influencing the circulation. Rain­ fine weather persisting over the next five days fall was 17 percent below normal with most fall­ except for squally showers on 15th as Typhoon ing in the early part of the month. Ed passed to the south of Hong Kong. However, as Ed turned on a more northwestward track The maximum temperature recorded on towards northern Vietnam one if its outer rain­ 1st, 30°C, the highest of the month, reflected the bands reached the coast on 19th bringing nearly fine weather which continued from the end of 100 mm of rain on that day. Thunderstorms also September. Easterly winds brought light rain occurred and the temperature fell to 23.9 °C, the early on 2nd and cloudy weather for the next two lowest recorded for the month. The next five days. With the landfall and dissipation of TD Ira days were characterized by periods of sunshine over Vietnam moisture and rain spread north­ interspersed with isolated light showers. A low wards to give two outbreaks of rain on 4th and pressure trough passed on the evening of 24th 5th. These produced about 95 mm in total with giving heavier rain and more thunderstorms the latter also being accompanied by thunderstorms. next day. The next three days were a combina­ A dry northerly airstream arrived on the night of tion of cloud, light showers and sunny intervals 5th and for the next seven days the daily mini­ before the last two days ended the month with mum relative humidity was below 60 percent. brilliantly fine weather. During this time fine weather prevailed apart from some drizzle early on 9th. With a return of Mean daily temperature 27.8°C (+ 0.3°C) moister conditions, cloud increased on 13th. Rainfall (provisional) 409.9 mm (128 %) However, with a persistent ridge of high pressure over eastern China, a fresh easterly airstream

34 HKMelS BULLETIN Vol. I, No. I, 1991 gave fine weather until 20th with only occa­ and lowering the temperature several degrees. sional light drizzle at night. Cloud returned on The dry northerly air stream resulted in the 21 st to be followed by three more fine days clouds thinning and sunny periods developing on with the weather warming up ahead of an 10th and 11th. For the next week windy condi­ approaching cold front. This front crossed the tions persisted as the northeast monsoon was en­ south China coast in the evening of 24th, hanced by the presence of tropical cyclones in the bringing some rain during the night. Cool South China Sea. First, TS Nell formed north of northerlies with cloud brought the temperature Nansha and moved towards Vietnam. During this down to a low of 19.7 °C on the morning of time the weather remained fine, though windy, 26th, the lowest for the month. Winds turned but as Typhoon Mike entered the South China easterly on 27th and apart from some light Sea clouds developed and rain fell in the after­ drizzle at night the weather remained fine for noon of 15th. On 16th, as Mike turned north the rest of the month. towards Hainan winds strengthened to reach an hourly mean maximum offshore of 80 km h-I in Mean daily temperature 25.1°C (+0.1°C) the morning of 17th. During this time there was Rainfall (provisional) 100.7 mm (83 %) nearly continuous light rain until warmer condi­ tions and fine weather returned on 19th. Tem­ peratures reached a high of 27.7 °C on 20th, the November maximum recorded for the month, but this warm • spell was brief as a cold front arrived that November was generally windy and evening. Fresh northerly winds and clouds re­ cloudy although, apart from an intense cold surge turned on 21st but the latter soon cleared to begin near the end of the month, the winter monsoon another fine spell on 22nd although winds did not did not bring low temperatures. The mean daily moderate till 23rd. The presence of Typhoons temperature was 0.8 °C above normal and the Owen and Page in the western North Pacific monthly mean minimum temperature of 20.4 °C continued to induce continental air flow leading was the fifth highest on record. Rainfall was only to a progressive fall in temperatures from 26th. slightly above normal. A major outbreak of cold air reached the coast in the evening of 30th bringing strong gusty winds, The fine weather which ended October hourly mean speeds of 90 km h-I being recorded continued for the first two days of November but at Tate's Cairn. Although the weather remained cloud and rain moved in from western Guang­ fine, both the relative humidity and temperature dong on 3rd. With easterlies freshening cloudy dropped sharply ending the month with a low conditions with persistent light rain, mainl y in temperature of 15.6 °C at midnight on 30th. the evenings, lasted for the next six days. A cold front crossed the coast in the morning of 9th Mean daily temperature 22.rC (+0.8°C) giving strong northerly winds and some light rain Rainfall (provisional) 36.9 mm (106 %)

HKMetS BULLETIN Vol. 1, No.1, 1991 35 Meeting Reviews

Dr. James R. Mahoney, Director of the Special Topics Lecture Series National Acid Precipitation Assessment Program (NAPAP), U.S.A. talked to members about the Venue: Royal Observatory, Hong Kong problems associated with acid rain in North America and the work of NAPAP. Date: 7 July, 1989

Two lectures were presented by distinguished visitors who were in Hong Kong in connection with the International Conference on East Asia Research Forum 1 and Western Pacific Meteorology and Climate held from 6-8 July and hosted by the Royal Venue: University of Hong Kong Observatory, Hong Kong and the Centre of Asian Studies, University of Hong Kong. Date: 30 September, 1989

Subject: Polar Orbiting Meteorological Satellite Subject: Modelling and Measurement Data Receiving and Processing System in China in Meteorology

Dr. Xu Jianmin, Director of the Satellite A successful inaugural research forum was Meteorological Centre, State Meteorological held at the University of Hong Kong, Rayson Administration, People's Republic of China, Huang Theatre on the theme "Modelling and talked to members about the Chinese meteorolog­ measurement in meteorology". The Opening ical satellite system, providing very interesting Ceremony and Welcome Address was presided information on the polar orbiting satell ite, FY 1, over by Chairman of the Society, Mr. Patrick the ground station and data processing centre, the Sham, who expressed the hope that this would be data receiving and processing system, and the the first of many to come since one of the most products available. important functions of the Society was to enable members to share and discuss ideas concerning Subject: Atmospheric Numerical Modelling for meteorology and related fields of endeavour. Weather Prediction The first session, on MODElLING STUDIES, Prof. T. N. Krishnamurti of Florida State was chaired by Dr. Steve Hsu of the Department University, provided members with the benefit of of Geography, The Chinese University of Hong his expertise in numerical modelling by talking Kong. about models and their limitations in weather prediction, particularly in tropical conditions. Two papers were delivered as listed.

STOCHASTIC MODElLING OF WIND AND Venue: Royal Observatory, Hong Kong TEMPERATURE

Date: 31 August, 1989 by Dr. Fred Hickernell, Dept. of Mathematics, Hong Kong Baptist College Subject: Acid Rain in North America

36 HKMetS BULLETIN Vol. 1, No.1, 1991 MODELLING ITPHOON SURGES IN WLO various components of the PEM , the different HARBOUR, HONG KONG airborne experiments being planned and their objectives in relation to the study of atmospheric by Dr. YC. Hon, Department of Mathematics, chemistry in the Pacific Basin, an area considered Hong Kong Baptist College ideal for conducting such experiments.

Following a break for refreshments the second session, on MEASUREMENT STUDIES, was chaired by Dr. Bill Kyle of the Department of Venue: Royal Observatory, Hong Kong Geography & Geology, University of Hong Kong. Date: 6 January, 1990

Two papers were delivered as listed. Subject: Coastal Protection Against Sea Waves

WiVE CHARACTERISTICS IN BEl BU WiN Prof. Patrick Holmes, Professor of Hydraulics in the Department of Civil Engineering and Dean by Dr. YS. Li, Department of Civil & Structural of the City and Guilds College, Imperial College Engineering, Hong Kong Polytechnic of Science, Technology and Medicine, U.K. ! talked to members about his experiences in coast­ TIlE COLLECTION AND ANALYSIS OF al protection. He is an international consultant on • WiVE DATA AT TIlE ROYAL OBSERVA­ coastal and offshore engineering problems involv­ WRY, HONG KONG ing wave action and his expert knowledge of wave processes and their engineering applications by Mr. T.S. Cheng, Royal Observatory, exposed members to a very interesting aspect of Hong Kong the relationships among meteorological and coast­ al processes, and architectural and engineering The forum concluded with an OPEN DIS­ design principles. In addition he presented some CUSSION in which the views of those attending interesting scenarios related to future coastal were sought concerning topics for future research protection in the light of potential sea level forums and an appeal made for any member with change associated with greenhouse warming. suggestions to contact the Executive Committee. The general consensus was favourable for contin­ uance of such forums and it was tentatively planned to hold a second in the spring of 1990. Annual Meeting 1990

Venue: City Polytechnic of Hong Kong

Special Topics Lecture Series Date: 23 March, 1990

Venue: Royal Observatory, Hong Kong Thirty two members and two observers partic­ ipated in the Annual Meeting of the Society held Date: 2 October, 1989 at 6:00 pm on Friday, 23 March, 1990 at the City Polytechnic of Hong Kong, Tat Chee Avenue, Subject: Global Tropospheric Experiment (GTE) Kowloon. The outgoing Chairman, Mr. Patrick and the Pacific Exploratory Mission (PEM) Sham, welcomed them and thanked the members of the 1989-90 Executive Committee for their Dr. Robert J. McNeal, Director of the Atmos­ hard work and the members of the Society for pheric Chemistry Program of the National Aero­ their support in the inaugural year of the Society. nautics and Space Administration (NASA), U.S.A. talked to members about NASA's GTE He then presented his annual report for 1989­ and PEM projects which aim to ask questions and 90 which highlighted the following points. At the test hypotheses on the role of aerosols and tropo­ end of February, 1990 membership of the Society spheric gases in influencing climate. Dr. McNeal stood at 131, comprising 82 Fellows, 43 Associ­ has vast field experience in the various GTE ate Members, 4 Student Members and 2 Corre­ programs, including the Amazon Boundary Layer sponding Members. During the year a logo for Experiment (ABLE) and gave members the bene­ the Society had been designed and adopted and fit of that as well as his expert knowledge in the ties bearing the logo had been made and were latest techniques for measuring trace gases and on available for purchase. During the year various tropospheric processes. He also described the activities of scientific and technological interest to

HKMetS BULLETIN Vol. 1, No.1, 1991 37 members and their guests were organized. These HK$150 for Fellow r included five lectures in the Special Topics Lec­ HK$100 for Associate Member ture Series given by distinguished visitors, two HK$ 50 for Student Member Research Forums, and a Visit to the Weather US$20 for Corresponding Member Station and Climatology Laboratory of the HK$500 for Institutional Member Chinese University of Hong Kong intended to stimulate the interest of secondary school stu­ dents. Several members of the Society were invited to present papers at the International Conference on East Asia and Western Pacific Research Forum 2 Meteorology Weather and Climate, the lectures of which were open to members. Venue: Hong Kong Baptist College

A review of intended activities in 1990-91 was Date: 24 March, 1990 then presented. In summary he concluded that the Society has had moderate success in its first Subject: Natural Disaster Reduction - the Role of year of existence with the growth in membership Meteorology and Hydrology in such a short time being better than expected and he hoped that member's interest in and A successful second research forum was held support for the Society would grow in the coming at the Hong Kong Baptist College with the theme year. being chosen to coincide with that of World Meteorological Day which was to introduce the The Hon. Treasurer, Dr. Steve Hsu, then 1990's as the Decade for Natural Disaster Reduc­ presented the audited accounts of the Society for tion. The Society was honoured to have Dr. the the year, which were adopted unanimously. Hon. Daniel Tse, OBE, IP; the President of Hong Kong Baptist College present at the Open­ Election of Office Bearers of the Society, and ing Ceremony and to deliver the Welcome appointment of the Honorary Legal Advisor and Address. Honorary Auditor resulted in the following: The first session, on A GLOBAL OVERVIEW, Chairman Mr. P. Sham was chaired by Dr. Fred Hickernell of the De­ Vice-Chairman Dr. W.1. Kyle partment of Mathematics, Hong Kong Baptist Hon. Secretary Mr. Y.K. Chan College. Hon. Treasurer Dr. S.1. Hsu Committee Dr. 1.C.L. Chan Three papers were delivered as listed. Dr. F. Hickernell Dr. Y.S. Li IN1ERNATIONAL DECADE FOR NATURAL Hon. Legal Ms. Venus Choy DISASTER REDUCTION - HOW METEORO­ Advisor LOGICAL & HYDROLOGICAL SERVICES Hon. Auditor Mr. 1.C.T. Wu CAN HELP

The major item of business was to consider by Mr. Patrick Sham, Royal Observatory, the proposed amendments to the constitution Hong Kong submitted by the Executive Committee. These were: to incorporate Institutional Membership in MONITORING HAZARDS IN tnt: NATURAL the Society; and to extend Student Membership in ENVIRONMENT USING METEOROLOGICAL the Society to secondary school students studying SATELLITES in Form 5 or above. After discussion and amendments to the original submission, both by Dr. Bill Kyle, Department of Geography and amendments were adopted and will be in force Geology, University of Hong Kong subject to the approval of the Registrar of Socie­ ties. ins IMPACT OF HOURLY GMS (GEOSTA­ TIONARY METEOROLOGICAL SATELLITE) The meeting agreed to continue waiver of the IMAGERY ON OPERATIONAL WEAmER Entry Fee for all those who submit their applica­ FORECASTING tion to join the Society in 1990 in order to en­ courage a growth in membership. The following by Mr. Edwin Lai, Royal Observatory, annual subscriptions for the year were also adopt­ Hong Kong ed:

38 HKMetS BULLETIN Vol. 1, No.1, 1991 Following a break for refreshments during Date: 24 June, 1990 which there was a Computer Display of METE­ OROLOGICAL IMAGE VISUALIZATION the THE THREAT OF THE GREENHOUSE second session, on NATURAL HAZARD REDUC­EFFECT TION IN HONG KONG, was chaired by Dr. Bill by Dr. c.x. Ng, City Polytechnic of Hong Kong Kyle of the Department of Geography & Geolo­ gy, University of Hong Kong. Date: 1 July, 1990

Two papers were delivered as listed. URBAN MICROCLIMATE by Dr. W.L. Chang, Royal Observatory, REDUCING THE THREAT OF FUTURE SEA Hong Kong LEVEL RISE Date: 8 July, 1990 by Mr. W.S. Yim, Department of Geography and Geology, University of Hong Kong NEW WEATHER EYES AND EARS by Mr. Edwin S.T. Lai, Royal Observatory, THE USE OF METEOROLOGICAL RADAR Hong Kong IN OPERATIONAL FORECASTING •! by Ms. Hilda Lam, Royal Observatory, Hong Kong Special Topics Lecture Series

Venue: Royal Observatory, Hong Kong

Popular Meteorological Date: 20 September, 1990

Lecture Series No.1 Subject: Visibility Study Programme in Connec­ tion with the Navajo Generating Station Venue: Hong Kong Space Museum Dr. Jerry L. Shapiro, of the Natonal Acid During the month of June and early July the Precipitation Assessment Program (NAPAP), Society co-sponsored with the Hong Kong Space U.S.A. talked to members about his work in Museum a successful inaugural series of popular connection with the air pollution and atmospheric lectures on meteorological subjects in Cantonese. visibility impacts of the Navajo electric power The subjects and speakers are listed below. generating plant in U.S.A.

Date: 3 June, 1990

TROPICAL CYCLONES - A CASE FOR THE Research Forum 3 DEFENCE by Dr. Johnny Chan, City Polytechnic Venue: City Polytechnic of Hong Kong of Hong Kong

Date: 10 June, 1990 Date: 10 November, 1990

HEAVY RAIN AND LANDSLIDES Subject: Engineering Applications by Mr. R.K.S. Chan, Geotechnical Control of Atmospheric Modelling Office, Hong Kong Government A third research forum was held at the City Date: 17 June, 1990 Polytechnic of Hong Kong with the theme being chosen to complement the 4th World Congress of EL NINO AND UNUSUAL WEATHER Council on Tall Buildings and Urban Habitat, by Mr. W.e. Lee, Royal Observatory sponsored by Hong Kong Institution of Engineers Hong Kong and held from 5 - 9 November in Hong Kong. The Society was honoured to have Dr. A.G. Davenport, Director of The Boundary Layer Wind Tunnel Laboratory, The University of

HKMetS BULLETIN, Vol. 1, No.1, 1991 39 Western Ontario, London, Canada present to Three papers were delivered as listed. deliver the Opening Address. THE EFFECT OF CLIMATE CHANGE ON The first session was chaired by Dr. Y.S. Li BUILDING DESIGN of the Department of Civil & Structural Engineer­ ing, Hong Kong Polytechnic. by Prof. A.P. Jeary, Department of Building and Construction, City Polytechnic of Hong Kong

Two papers were delivered as listed. APPLICATION OF ENVIRONMENTAL DATA IN MARINE WORKS DESIGN COMPUTATION OF STRATIFIED FLOW PASTA HIlL by Mr. 1. Gabay, Port Works Division, Civil Engineering Services Department, Hong Kong by Dr. S.c. Kot, Department of Mechanical Government Engineering, University of Hong Kong THE ROLE OF ME1EOROLOGICAL DATA CORRELATION STUDIES ON RAINFAIL IN WATER QUAL/IT MODEUJNG INIENSITIES AND SLOPE FAILURES by Dr. 1.H.W. Lee, Department of Civil and by Dr. J. Premchitt, Geotechnical Control Office, Structural Engineering, University of Hong Civil Engineering Services Department, Hong Kong Kong Government

Following a break: for refreshments the second session was chaired by Dr. S.c. Kot of the Department of Mechanical Engineering, Univ­ ersity of Hong Kong.

40 HKMetS BULLETIN Vol. 1, No.1, 1991 Calendar of Coming Events

This section is intended for the publication offorthcoming Hong Kong, April events organized by the Society or by other organizations with similar aims. Ifmembers wish to notify the Society of 2nd Hong Kong Meteorological Society Annual Meeting. any such events they should mail or fax such information to the Editor-in-chief along with their name(s) and membership Trieste, Italy, April 8 -12 number(s). World Meteorological Organization Technical Conference on

1991 "Long-range ~ather Forecasting Research H.

New Orleans, USA, January 13 - 18 Cairo, Egypt, April21- 27 7lst American Meteorological Society Annual Meeting. International Symposium on "Geophysical Hazards in 1st American Meteorological Society Symposium on Developing Countries and their Environmental Impacts". "Winter Storms". London, England, April 24 2nd American Meteorological Society Symposium on "Global Change Studies ", Association of British Climatologists Meeting on "Current Climatological Research in United Kingdom". 7th American Meteorological Society Symposium on "Meteorological Observations and Instrumentation ". Geneva, Switzerland, May 1- 26

7th American Meteorological Society International Confer­ 11th World Meteorological Congress. ence on "Interactive Information and Processing Systems for Meteorology, Oceanography and Hydrology ", MiLlmi, USA, May 6 -10

7th American Meteorological Society Joint Conference 5th American Meteorological Society Conference on with Air and Waste Management Association on "Meteorology and Oceanography ofthe Coastal Zone ", "Applications ofAir Pollution Meteorology". 19th American Meteorological Society Conference on Male, Maldives, January 29 - February 4 "Hurricanes and Tropical Meteorology ".

18th Session, WMO/ESCAP Panel on Tropical Cyclones. Hong Kong, June

Hong Kong, March Hong Kong Meteorological Society and Hong Kong Science Museum Popular Meteorological Lecture Series. Hong Kong Meteorological Society and Hong Kong Space Museum Popular Meteorological Lecture Series. Paris, France, June 24 - 28

London, England, March 22 4th International Conference on "Aviation ~ather Systems". 25th International Conference on "Radar Meteorology ", Royal MeteoroLogical Society Meeting at The Royal Society on "Computers in Meteorology & Oceanography".

HKMetS BULLETIN Vol. I, No. I, 1991 41 Keele, England, August 5 - 7 Sou Lake City, USA, September 10 - 13 1I Royal Meteorological Society Summer Meeting at the 7th American Meteorological Society Conference on I, University of Keele on "l\t>ather Forecasting - Science "Applied Climatology", and Art". 10th American Meteorological Society Conference on Vienna, Austria, August 11 - 24 "Biometeorology and Aerobiology ".

20th International Union of Geodesy and Geopphysics 20th American Meteorological Society Conference on General Assembly. "Agricultural and Forest Meteorology ",

42 HKMetS BULLETIN Vol. 1, No.1, 1991 L HONG KONG METEOROLOGICAL SOCIETY

Office Bearers: Mr. P. Sham (Chairman) (1990-1991) Dr. WJ. Kyle (Vice Chairman) Mr. Y.K. Chan (Hon. Secretary) Dr. S.S.!. Hsu (Hon. Treasurer) Dr. lC.L. Chan Dr. FJ. Hickernell Dr. Y.S. Li

ThWORMATIONFORCON~UTORSTOTHEBULLETIN

Technical or research articles, as well as reviews and correspondence of a topical nature are welcome. In general contributions should be short, although exceptions may be made by prior arrangement and at the discretion of the Editorial Board. Copyright of material submitted for publication remains that of the author(s). However, any previous, current or anticipated future use of such material by the author must be stated at the time of submission.

Manuscripts must be accurate and preferably in the form of a floppy diskette containing an electronic version in.one of the common word processing formats such as Word, Wordstar or Wordperfect. Whether or not an electronic form is submitted, two complete printed manuscript copies of the article should be submitted. These should be preceded by a covering page stating the title of the article, the full name of the author(s), identification data for each author (position and institution or other affiliation and mailing address). An abstract of.about 150 words should be included. Manu­ scripts should be double-spaced, including references, single side only on A4 paper with a 2.5 cm margin on each side, and be numbered serially in pencil.

All references should be arranged in alphabetical and chronological order. In the text, in brackets, author's surname(s) followed by the date; in the reference list at the end, the author's surname(s) and initials followed by the date and the title of the work. If a book, this should be followed by the publisher's name, place of publication and number of pages; or, if a journal arti­ cle, by the title of the periodical, volume and page numbers.

Originals of tables should be neatly drawn as they will be reproduced directly. Diagrams should be in black on tracing material or smooth white paper, with a line weight suitable for any intended reduction from the original submitted size. Black and white photographs should be clear with strong contrasts. Colour photographs are also acceptable by prior arrangement with the Editorial Board. Please contact the Editor-in-chief for details. Originals of all illustrations should be numbered consecutively with captions printed on separate sheets of paper and should be clearly identified with the author's name(s) on the back. All copyright materials to be published must be cleared by the contribu­ tor(s).

The principal author will be sent proofs for checking prior to publication. The Society does. not pro~ide authors with free offprints of items published in the BUlletin, but may be able to obt~m quotations on behalf of authors of technical articles who express, at the time of submission, a Wish to purchase offprints from the printer.

Enquiries and all correspondence should be addressed to the Editor-in-chief, Hong Kong Meteorological Society Bulletin, c/o Department of Geography and Geology, University of Hong Kong, Pokfulam Road, Hong Kong (Telephone: (852) 859-2831; Telefax: (852) 559-8994; email: [email protected]). HKMetS BULLETIN, Vol. 1, Number " 1991

HONG KONG METEOROLOGICAL SOCIETY BULL I

CONTENTS

Editorial 2

Research in the atmospheric sciences in Hong Kong - a proposed agenda 3 Johnny C. L. Chan

"SPECTRUM" : typhoons under critical examination 7 c.y Lam

Storm period variation of rainfall pH: the example of Typhoon Brenda, May 1989 10 Mervyn R. Peart

An analysis of tide gauge and storm surge data in Hong Kong 16 Wyss W.S. Yim

News and Announcements 24

Correspondence 26

Hong Kong Weather Reviews 27

Meeting Reviews 36

Calendar of Coming Events 41